I think "is" is a good translation for 'является'. However, the usage of that word in Russian is different from English. English makes use of "is" as an auxiliary verb, but there are no auxiliary verbs in Russian. That, I think, is the source of your confusion making you think the present tense of 'is' is not used in Russian.

If you want to say something like "This book is excellent," you would translate that into Russian as "Эта книга замечательная," omitting the auxiliary verb "is". And, technically, you could use 'является' here: "Эта книга является замечательной."

However, Russians in that situation would prefer saying something more elegant like "Это замечательная книга", avoiding the use of 'is' and the verbose form altogether.

So, what would be the correct usage of 'является', might you ask. I think the usage should be much closer to "would be".

Чем же является на самом деле эта книга? => What would the book really be?
Эта книга является энциклопедией нашей жизни. => The book would be the encyclopedia of our lives.

vs.

Что же такое на самом деле эта книга? (Somewhat awkward in Russian.) => What is that book really?
Эта книга - энциклопедия нашей жизни. => The book is the encyclopedia of our lives.

Close, but not the same.