Google services like Gmail, Google Calendar, and Google Contacts are incredibly popular and, what's more, are incredibly easy to setup on your iPhone or iPad. If you have a free Gmail account, you can set it up through the iOS Settings app and access it through the built-in Mail, Calendar, Contacts, Reminders, and Notes apps. You can also setup Gmail inside Google's own Gmail for iOS app. If you have a paid Google account, you can use either of those options, or you can use Google Sync, Google's implementation of Microsoft's ActiveSync service. (Sadly, Google discontinued ActiveSync support for free accounts in 2013).
How to setup Gmail, Google Calendar, and Google Contacts in Settings
The iOS Settings app, Mail, Calendar, and Contacts section contains built-in support for Gmail, Google Calendar, Google Contacts, and related services. Under the hood, Apple is using the open standard IMAP, CalDAV, and CardDAV services to handle the syncing. Unfortunately, Gmail retro-fitted support for IMAP and it's quirky at times. However, if you want to use the built-in iOS Mail app and its unified inbox, and don't have a paid account, it's your only option.
- Launch Settings from your Home screen.
- Tap Mail, Contacts, Calendars.
- Tap Add Account...
- Tap Gmail.
- Enter your name, Gmail email address, password, and a descriptive name (like Gmail, or Personal, so you can identify it later).
- Select which services you want to leave on for sync, Mail, Calendars, and Notes. (You probably want all of them on.)
- Tap Save.
How to set up Gmail's 2-step verification
If you're worried about your Gmail security, you can also setup and use Gmail 2-step verification on your iPhone, iPod touch, or iPad. For most people, it's probably more trouble than it's worth, but it's there for those who really need it.
How to add a Gmail or Google apps account to your iPhone or iPad using an app-specific password
If you have a Gmail or Google apps account that has two-step verification enabled, the process of linking your account to your iPhone or iPad is slightly different, as you may have found out if you attempted to sign in and got an incorrect password error. This is because you'll need to generate an app-specific password for your iPhone or iPad in order to securely link them to your Gmail or Google Apps account.
How to setup Gmail, Google Calendar, and Google Contacts using ActiveSync
Google licenses ActiveSync for Google Sync, which used to be available for all Gmail accounts but is now restricted to paid Google accounts. You don't get Notes sync when you use Exchange, but you do get incredibly fast email.
How to setup Gmail in the Gmail app
Setting up Gmail in the Gmail app gives you the complete Google email experience, but it doesn't give you Google Calendar or Google Contacts, or anything else. If you want to use the Gmail app, the good news is it's ridiculously easy to setup — just download and launch. However, you'll either have to setup your Google account in Settings (see above) or setup things like Calendar specifically using CalDAV.