Okay I understand that u have been training for a long time or just started training so there is a little advice for u. Exercise that u should be performing in gym.

1. Squats
   One of the best exercise that targets almost every muscle of ur body. Especially ur core, quads hamstring and glutes.
2. Deadlifts
   As the name given it looks easy before mastering and believe me once u master it voila it will be a piece of cake. Legs and back are the muscles that are targeted.
   3.Dumbell bench press
   Many will not agree but after doing u will find that dumbell bench presses are very effective than normal rod bench presses

Bonus
Pushups and pullups
These are the exercises that I find most important if u r into fitness because these are capable of creating ur upper body

If u want any other type of info do comment and also comment if u r going to the gym or any kind of fitness related activity and r u doing anyone of these.