If you are using Android device then you need to set up and link the device to Google account. In case, if you want to add another Gmail account then check out the steps mentioned below to know
how to sync Gmail on phone and laptop. Start by opening the native Gmail app and then click on three menu icon at the upper-right corner of the Gmail app. Scroll down the page and click on add account. Choose Google as account type and click on OK. Tap to existing to sync with an existing Gmail account. Lastly, enter Gmail address and password in the requested field to successfully setup Gmail account.