Is Someone else using your Gmail account? Or how many devices are logged in to your Gmail? How to find out, know the whole process

Step 1: Open the Gmail app on your Android Smartphone or Tablet.
Step 2: Tap “Add Account” if you are not signed in. If you are already signed in to another account, tap your profile picture at the top-right corner, then tap “Add another account”.
Step 3: Choose Google as the account type.
Step 4: Enter your Gmail Address or Phone Number, tap “Next.”
Step 5: Enter or Make your Strong Password, tap “Next.”
Step 6: Follow any all Additional Verification steps if required.
Step 7: You are Now Logged in and can access your Gmail inbox.