Hi and welcome.

The current standard for uvb lighting is a T5 with either a 5.0 or 6% bulb. The fixture needs to be long enough to span the width of the enclosure. Since the enclosure you have is a bit small and will need to be upgraded to at least the minimum 2x2x4’, I advise getting a 24” long light. If the chameleon you have is a baby or young one, you’ll want to elevate your lights off the screen top to prevent burns when little one is walking upside down along the top. Just a couple of inches is enough. Then, you’ll want to set up your basking branch about 8-9” below the lights.
I’m very glad that you included a pic as the ivy plant that you have is toxic. A much better plant is pothos. Veiled chams will eat their plants, so it’s important that they be safe, real and washed of any chemicals. You’ll want to set up a nice network of branches and vines for your cham to travel. It is a challenge to attach things to screen. You’ll want to set up and create either a little scaffolding type thing, using the frame to bear the weight and make attachments to. Another good option is a small garden trellis, again, attached to the frame. When you upgrade, these are incredible and can handle plants and just so much weight.
Rather than talk your ears (eyes?) off, let me give you some links that will help you get the basics down.
https://chameleonacademy.com/chameleon-basics/ If you prefer video, check out Neptune the chameleon on YouTube. Neptune has partnered with Pangea reptile and created a correct chameleon kit and the price is amazing! You’ll spend so much more than that buying things individually.
We love helping new keepers get everything as perfect as possible for their amazing new scaled friend, so ask whatever other questions you may have, share your ‘journey’ or just whatever you’re comfortable with. I’m very glad that you found your way here.