Should we do cardio right before our workout?i read that it causes muscle loss, should it be done before if your goal is to gain muscle and lose fat.

Gain/lose muscle: Although this is a rather complex issue, my recommendation is to use your workout to either build mass OR increase cardiovascular ability. Heavy weights/low reps tend to build muscle. Low weight/high reps tend to burn calories and help endurance. You're likely to find that trying to do both in one workout will leave you achieving neither goal, feeling exhausted and frustrated with lack of progress