Tattoos - These are self-explanatory for anyone who lived in the twentieth century. Ink of various colors are injected into the skin via fast-moving needles. It can be relatively painful depending on where the tattoo is. In my experience (five tattoos) the most painful place I've had tattooed is my upper back. Between the spine, the ribs, and the shoulder blades it doesn't make for a very pleasant experience, but the result was so worth it (see picture above). And for all the people asking "How can you do that to yourself?" the answer is simple. If you take care of a tattoo correctly, which can take up to two weeks of constant care, by the time it's healed it feels like you've had it all your life and it fully becomes a part of you and not just your skin. Not to mention they are completely addicting, thus the reason why I've gotten five within a span of three years.
Piercings - Yet again a pretty straightforward bod mod. A long needle gets stuck through your ears, tongue, lip, nose, or wherever else you might want one, and a ring is slipped through it (rings are preferable since they're easier to clean and less prone to infections). Then the healing time varies depending on where the piercing is. For a full list of rough healing times you can go here. Keep in mind healing times depend on how well you take care of the piercing. For pretty much any piercing, I recommend a product called H2Ocean. It's a premixed formula of salt water (the best option to keep new piercings clean without irritating it) in a convenient spray canister and can even be used on oral piercings.
Scarification - This is one of the lesser-known bod mods. Again, it's a simple idea, just a little more cringe-worthy, even for me. The basic idea is to make a deep enough mark in the skin so that it leaves a scar in a designated style. This isn't nearly as predictable as tattoos or piercings just because of all the different factors there are, like skin thickness. For more info i recommend this page.
Branding - This goes along with the scarification and it's applied exactly how you think it supposed to be. A mark is burned into your skin. This is one that I personally wouldn't try, just because I don't like extreme heat or cold (yeah, it can be done with extreme cold too). If you want to get more extensive check out this page.