If you have a Gmail account, you can access it on your iPhone using Apple's Mail service or the Gmail or Inbox apps, which are official Google apps.
Steps
Method 1 of 2: Add an account to Apple's Mail app

Step 1. Open settings
Tap the gray cog icon (⚙️). Usually it is on the home screen.

Step 2. Tap Mail
This option is in a section with other Apple applications, such as Calendar and Notes.

Step 3. Select Accounts
This is the first part in the menu.

Step 4. Tap Add Account
You will find this option at the bottom of the section Accounts.

Step 5. Select Google
You will see the option in the middle of the list.

Step 6. Enter your address
Type your Gmail address in the field provided.

Step 7. Tap Next
It's the blue button on the screen.

Step 8. Type your password
Enter it in the indicated field.

Step 9. Tap Next
It's the blue button on the screen.
If you've enabled Google two-step verification, enter the verification code you received via text message or with the Authenticator app

Step 10. Activate the account
Slide the button in front of the option Mail to the right to activate it. It will turn green.
Choose the other Gmail data you want to sync with your iPhone by sliding the button in front of each option to the activated position (it should turn green)

Step 11. Press Save
It's at the top right of the screen. You can now send and receive emails with your Gmail account through the Mail app on your iPhone.
Method 2 of 2: Use the Gmail or Inbox app

Step 1. Open the App Store
Tap the white A icon in a white circle on a blue background.

Step 2. Search for Gmail
Press on To research at the bottom of the screen and start typing "gmail" in the search box that appears. As you type, suggested applications will appear on the screen below the search bar.

Step 3. Choose an application
Gmail and Inbox by Gmail are official Google applications that allow you to send and receive messages with your Gmail account on your iPhone.
The main difference is that the Inbox app also allows you to use accounts other than Gmail

Step 4. Tap Get
The option will appear to the right of the application.
When the button displays the word "Install," tap it again. The app icon will be added to your home screen

Step 5. Tap Open
This word will be displayed in the same place as the “Get” and “Install” options.

Step 6. Tap Allow
This will allow the app to send you notifications when you receive emails.
- If you are using Inbox and not the Gmail app, you will need to identify yourself before activating notifications.
- You can change these settings by opening your iPhone settings and selecting Notifications, then Gmail Where Inbox.

Step 7. Tap Login
This button is located at the bottom of the screen.

Step 8. Activate your Gmail account
If you see it in the list of accounts, drag the button to the activated position (it will turn blue).
- If you don't see your account, tap Add an account at the bottom of the list. Enter your Gmail address, tap Following, enter your password and press Following.
- If you've enabled Google two-step verification, enter the verification code you received via SMS or with Authenticator.

Step 9. Tap Done
The option is located at the top left of the screen. Your Gmail account is now registered in one of the official Google applications on your iPhone.
- To add or edit Gmail accounts, tap the icon ≡ at the top left of the Inbox app, tap the down arrow to the right of your Gmail address and press ⚙️ Manage accounts.