"It is a quiet park."
Translation:Это тихий парк.
Look in the forums here, you should find some useful things there. Also the grammar tips on the relevant lessons.
This one here is quite simple - it is the prepositional case which is used with nouns after some prepositions (in, on, to etc.). The most common ending for this case is the addition of an е - as in the case with парке - or that the final vowel of the noun changes to е... For example: место (place) becomes месте in the prepositional.
I'm a learner like you, so I don't know the other changes that occur in this case, and I don't know the exceptions - I just wanted to give you that tip.