Hi Msfatima.I hope it's not too late.as others said adjectives always don't come after nouns in general;but in your level of learning you just need to know these three forms(I think):
-use adjectives after nouns :رستوران خوب (good restaurant),گل زیبا (beautiful flower)
-use them after nouns for "Comparative" uses : رستوران بهتر (better restaurant),گل زیباتر (more beautiful flower)
-use them before nouns for "Superlative" uses : بهترین رستوران (the best restaurant), زیباترین گل (the most beautiful flower)
Good luck