For seated dips you need a bench in the park or other object you can sit on. This exercise is relatively easy and a great way to train you triceps.
How to perform seated dips
When you sit on the park bench, then place your hands on the seat next to your hips. Allow your fingers to hang over the edge. Keep your knees bent and feet flat on the ground to make the exercise easier, or straighten your legs and rest your heels on the ground. Support your weight in your arms as you lift your hips up and forward off the bench. Inhale, bend your elbows behind you and lower your torso until your upper arms are parallel with the ground. Exhale, straighten your arms and return to the starting position.