To modify a noun, if the noun has ה, then the adjective needs ה as well. If the noun doesn't have ה, don't add it to the adjective.
To make a declarative sentence, - if the noun has ה , just use the adjective and your sentence is declarative. If the noun doesn't have ה, then you need a copula to connect.
So for this case: בננה טעימה=a tasty banana the tasty banana=הבננה הטעימה הבננה טעימה = The banana is tasty בננה היא טעימה = A banana is tasty