Please help I cannot build the android apk, I tried today before too, it was working fine but now its not building the app.
Thanks in advance 
Read what the error message says, do what it tells you to do. Problem solved.
Please do not post text as images: You should really post the plain text error message (instead of a screenshot and image of it) so that a) someone can copy/paste the error message to Google or something like that trying to help you and b) this forum post itself will be findable by using the forum search engine or Google later. Thank you.
But how I didnt get how to do that, please help.
Open Android Studio, open the SDK Manager, accept the terms.