In this post, i'm going to explain everything you need to know about Pokémon GO.

How do i start?

First of all - make sure that you meet the phone requirements.

Android

Android 4.4 to Android 6.0.1 (Android N will not supported until the official Android release)
Preferred resolution of 720x1280 pixels (Not optimized for tablet)
Strong internet connection (Wi-Fi, 3G, or 4G)
GPS and Location Services

iOS

iPhone 5+
iOS 8+
Strong internet connection (Wi-Fi, 3G, or 4G)
GPS and Location Services
Jailbroken devices are not supported

Here are the links for the app
Android
iOS

Make sure that you are able to find the game in your Google Play or App Store. If you can't find the game - don't worry, i have a solution for you.

For Android users, the simplest thing to do is to download the game from APK Mirror. APK Mirror is run by the people behind AndroidPolice.com, so i think you don't need to worry.
APKMirror
Before downloading, make sure to allow your phone to install third-party apps. In Settings, find the Security tab and allow "Unknown Sources".

For iOS users, the easiest way is to create another AppStore account, located in USA. You should go to Settings, select iTunes&AppStore and sign out of your current account. Once you've done it, go to General and find Language & Region tab. Set your region as US. Now, go to AppStore, choose any free app and download it. You will get a pop-up, which will ask you to login into your existing account or create new. Simply create new account. You are able to proceed without any payment methods, just choose "None".
Note: make sure that you address, state and number are all good. Use randomlists. Don't forget to sync your phone number with the chosen state. For that purpose, use fakenumber. Be sure to use the area code of the chosen address.

After downloading the game, use your regular account. Your apps won't be gone.

I got the app, what's next?

Make sure you have your location services enabled. Allow Pokémon GO to use them. Check your internet connection and you are good to go!

Use your Google account to log in. You can use your Pokémon Trainer Club account as well.

Done!
Great! Now the game will guide you through the basics of Catching Them All!

I caught my first Pokémon!

Congratulations! Now it's time to share some tips with you:

You can make your Pokémon evolve or be upgraded. Every upgrade consumes a selected Pokémon candy and some Stardust. Evolving requires a big amount of candies. Every time you catch a Pokémon or transfer your Pokémon clones (mostly low level) - you get some candies.
You are level 5? Time to choose your team: Team Instinct, Team Mystic or Team Valor. The game will guide you through the process of choosing your team.
No, you cannot battle other players directly yet. However, you are able to battle their Pokémon at your local gyms. Gyms are special points of interest found throughout the world. You can capture a Gym for your Team and battle the Pokémon of rival Teams there. Gyms can be challenged by multiple Trainers at the same time. A Gym’s level is determined by its prestige. As a Gym earns prestige, it increases in level. The higher a Gym’s level, the more Pokémon can be assigned to it, which makes it harder for rival Teams to capture. A Gym’s prestige increases when you assign a trained Pokémon to it, and also when teammates assign additional Pokémon.
Don't miss PokeStops! PokeStops are places in Pokemon Go that allow you to collect items such as eggs and more Poke Balls to capture more Pokemon! After level 5 you may find various interesting consumables, as Pokémon eggs, pokeballs, potions, incense, etc.

Here are short descriptions of each item:

Pokéball: you catch Pokémon by throwing Pokéballs at them. Easy to find at PokeStops.
Lucky Eggs: get double the experience you normally get. Rare to find, easy to buy and you'll be given some during your game.
Pokémon Eggs: common item, found at PokeStops. Hatch your eggs and walk - you will get a Pokémon after the certain amount of KMs/miles. You can hatch in your Pokémon menu.
Potions: used to restore your Pokémon HP after battles. Please note, that you don't loose your Pokémon.
Lure modules: attract Pokémon to the PokesStop you've attached the module to.
Incense: become a Pokémon magnet.
Razz Berries: make it easier to catch a Pokémon
Egg incubator: used for hatching
Revive: revives your Pokémon.

You will have each item at least 1-2 times, so it's not necessary to buy coins.
If you are willing to find Pokémon fast all the time, then invest in Lure modules, Razz Berries and Incense. Simply use incense while walking around and looking for Pokémon, set a Lure module at your favorite PokeStop and use Razz Berries to catch Pokémon with a high CP. Please note, that at level 20 you'll be introduced to another kind of Pokeballs.
The CP is generally how cool your Pokémon is. Higher the CP - harder to beat.
Always pay attention to your surroundings. Virtual creatures aren't worth your life. Do not visit potentially dangerous areas, don't use AR in the areas where it's not allowed to take photos or videos, remember about the people surrounding you. Hint: you can play without the AR, so you don't need to use your camera.
Save your battery by not using AR and switch on built-in battery saver mode. You can do it in-game, just tap the gear in menu.

My game is frozen/i can't log in/my GPS is not working.

Restart the app, reboot the device. Check your internet settings, check your GPS settings. You'll have to restart the game a lot, as the game is still not perfect.

I've found a cool hack, i'm the owner of everything in Pokémon GO, yeah!

Glad to hear it. But remember: there is a huge possibility of getting banned by using hacks or GPS spoofing.

Here's a bonus for you: how to catch Pikachu at the very beginning of the game (taken from Polygon):

When Professor Willow tells you to go choose your starter, the initial trio will spawn on the in-game map. Typically, clicking on one initiates a battle, resulting in you obtaining your first Pokémon. If you don’t select a Pokémon, however — if you just keep walking away instead — the three will disappear, then respawn in front of you. This is a little tricky to work out, since the game’s camera keeps the trio on screen with you for most of the time, and its GPS still isn’t the most accurate. But if you manage to ignore Charmander, Squirtle and Bulbasaur four times, they’ll come back with another friend in tow.

Hope that helps. In the next Pokémon GO post, i'll share my thoughts on Pokémon upgrading and evolving.