The glute bridge is an easy to perform glute isolation exercise.
This exercise is also similar to a hip thrust. Incidentally both exercises are easily progressed by adding weight.
For further reading on the differences see; Glute Bridge vs Hip Thrusts.
Start by lying flat on a mat with your knees bent and feet firmly on the floor.
Keep your hands by your sides and drive through your heels bringing your hips as far off the floor as possible. Squeeze your glutes at the top, pause and then lower yourself back down through the same controlled movement. Go for reps.
Progress your glute bridge by resting a barbell across your hips and taking the additional weight through the same movement.
To further progress this move, consider moving onto hip thrusts.
While doing the exercise is far better than not doing it (in most cases), it should be noted that sloppy form on any exercise is not recommended. If you are performing your glute bridges with incorrect form, you may recruit other muscle groups during the exercise, or poorly engage the intended muscle groups, which will hinder your gains at best and result in injury at worst.
In addition to your glute bridges, you should also consider your overall bigger picture. How many reps and sets you perform with each exercise depends entirely on where you are physically and of course, your desired outcomes.
Check out more bum exercises and of course, be sure to track your lifts.