My phone needs me to sign in to Gmail, however, when I do it says my password is invalid. I have my service through Straight Talk and I cannot use the phone because it will not let me bypass the need to sign in. I called Straight Talk and they said I had to talk to someone from Gmail.
Straight Talk is only the service provider so they would not have any need for you to sign into Gmail. This requirement most likely means that you are using an Android device. Android is the operating system that is provided from Google which in turn means that the OS is gathering and storing data and other content under your account. This means that you need to sign into google services to use most of the features within the operating system.
Since you are having trouble signing into your device then you should check a few things to narrow the actual problem.
The first thing to do is to try and sign into your account from a known good location such as your home computer. This step will allow you to find if your password is correct or if you are mistaken. Also if the account is locked out or you have your password incorrect you will be able to start the password reset process from here.
The second thing to check if your password is actually correct is to check if you have Two-Step Validation enabled on your account. If you do have this enabled you may need to first validate the new sign in as it is coming from a new unknown location.