You need to get a soundbar that fits in the space you have available. Some people have their TV mounted and a soundbar could happily be mounted underneath. Others have their TV on a stand and the soundbar can sit in front of it.
Consider the space you have free but also the size of your TV. A compact soundbar might look silly with a massive screen and vice versa. There are many different-sized soundbars available to suit your TV, so make sure you check the dimensions and match them up.