"My work is very important."
Translation:Моя робота дуже важлива.
I tried to find some definitions that would clearly show the difference, but I failed. In general, праця has slightly broader meaning than робота, but often they can be interchanged. Typically, we say робота to mean job and in that meaning it is rarelly can be substituted with праця. But when we speak about activity of doing something you almost always can choose any of the words.
Verb "працювати" which is derived from праця is often trnslated to English as "to work" and "робити" (from робота) is often do or make in English
If you want to use the copula "є," then "Моя робота є дуже важливою" sounds better. Usually "є" is not used.