Which is the best database connection mechanism to be used for an Android app?

I am new to android development, a noob precisely. i started android just last year and i am so confused on what database connection mechanism type to be used with my android for its Login and Signup Functions. i have searched online and came across couple of methods like (SQlite, MySQL, Volley, etc...) but i don't know which is better to learn and integrate with my Android APP.

So if anyone can just help me out with making this choice!

Also, links to documents, tutorials or any relevant resource would be appreciated !

Thanks.