Lamb Boy,
Because you posted an image of a simple belt, I would recommend the following materials to make this as simple a project as you can, then you can get fancier as time goes on and you get the basic idea of a belt.
Leather: Start by purchasing pre-cut belt strips. The one in the image is a 1.5 inch, more than likely 9-10oz., which is a very common size for belts, especially the trendy ones that Tanner Leather Goods and other companies put out. I'm not saying thicker isn't better, because it is obviously stronger, but for a simple belt that you would wear day to day that is just holding your pants up, 9-10oz. is more than enough. If you cannot find any pre-cut strips, buy a Strip Cutter. These things will save your life. I put off buying one for a long time, and when I finally bought one, my productivity skyrocketed. You can also purchase Belt Blanks, which come with everything cut out for you. It would remove the need for a few of the latter tools.
Buckle: The buckle should be solid, as the guys above me mentioned. No one likes a two toned metal after wear and tear. I get mine from Oregon Leather Company, but it seems they do not carry the ones I get online. From my understanding, I use the same ones as Filson does on their belts.
Rivets: For starters, stick to copper rivets. They are easier to use and strong as hell. Eventually you can spend the money to get a press, then it makes sense to use a double cap rivet because it's more efficient. For the copper rivets you should start with a size 8, 9 or 10. 12's are a bit small aesthetically, but they will still do more than hold your buckle on. You'll also need a farmer's rivet setter.
Cutting Tools: For cutting the ends of the leather you'll want a Strap End Cutter. You can get these in a variety of shapes, so do some browsing to find what you want here. You will also want a Revolving Spring Punch. This will give you a few options for punch sizes. You will use it for your rivet holes and buckle holes at the end of the belt. For the hole that the buckle goes through, you will need an Oblong Punch. I would recommend one inch for the length. That should give you clearance for most buckles.
Sizing: Some notes on sizing. For a belt, you will want to measure the distance around your or your clients waist. Take that measurement and add two inches, and that will be the length of the belt from the bottom of the buckle. You can check out this chart to get a better idea (click on the customer service link to view the chart). You will punch five holes at the end of the belt, each being one inch apart. You will do your first hole 4 inches from the tip of the belt, and then punch the remainder towards the buckle.
It's a straight forward project, so I wish you luck! Hopefully you can get all the leather and tools you need to make it happen! If you have any questions, let me know. I think I got everything in here, but I could have overlooked something.
Cheers,
Stephen
www.blkancr.co