What it means
しょうがない means that a situation cannot be changed or avoided, so there is no useful action left to take. It often expresses resignation, acceptance, or mild frustration, and can be used by itself or after a situation that has led to an unavoidable result. The expression is relatively casual; しょうがありません is a polite counterpart.
Usage note
しょうがない does not mean that something must be done. Do not treat しょうがないといけない as a standard obligation expression; the obligation pattern is 〜ないといけない.
How to use it
Clause (plain form)しょうがありません
道が閉鎖されているので、しょうがありません。
Since the road is closed, it cannot be helped.
Clause (plain form)しょうがない
道が閉鎖されているので、しょうがない。
Since the road is closed, it cannot be helped.