To secure your google account, enabling the 2 step verification feature on your google account is highly recommended. With this feature, not just anyone can access your Google account, even though the person knows the address along with your email password.
Every time someone logs in to your gmail account, google account sends you a verification code via SMS or phone. So the person who wants to login to your google account without entering the verification code will be rejected and can not log into your account. To enable this 2-step verification feature, you must first add an active mobile number (your own number, not others). If you have not added it yet, you can read the tutorial here.
After that, consider the steps below for how to enable 2 step verification google account.
1. Login to your google account via the following link.
So every time someone else logs in to your Google account from an unknown device, this 2-step verification page should appear and even if the person knows your email address and password, it will be difficult to enter the verification code first if you want to login.