Oopen up the Gmail app. . If you are not already signed in, you will get the Google sign-in page. Enter your Email address and your Password. You can aslo get help is you forgot your password. After you sign-in, on the screen that comes up, there is on the top left of the screen a square of three lines . Tap this. Next tap the downward arrow on the dark gray screen that comes up. On this page is listed the Gmal accounts that currently able to be used. Tap the account that you want. If for some reason you cannot see your account, just go to the the "mangage accounts" screen at the bottom of the screen. (You might have to scroll to get to it.) When the "Accounts" screen where you can select the account that you want appears, select "Add another account". Now a "Sign in" page shows up. Enter your e-mail address and your password. This should get you signed in.
If you want to add another account, tap "Add another account". Now you will go to the "Sign in with you Google account" page that has at the bottom "Create an account" Tap this. Then follow the instructions on the "Create your Google Account" page. Now just enter the account information that you want to use.
Alternatively, to sign-in into a Gmail account without going through the Gmail app,, go to http://www.google.com/accounts
. There you will get the sign-in page for Gmail. Enter your Email address and your Password. You can aslo get help if you forgot your password. Additionally, you can create a now account by tapping "Create an account" at the bottom of the page. Then follow the "Create your account" page's instructions