Before you start buying a ton of vinyl for your new Cricut or Silhouette machine, it pays (or really saves you money) to know what vinyl is what. This post will just cover basics to give you an idea of what to buy based on the types of projects you want to complete!
Heat Transfer Vinyl
First, the terms: Heat transfer vinyl, HTV, iron-on. These are all the same and used interchangeably in the Cricut crafting community. This is the stuff you'll need an iron, Easy Press, or heat press to adhere to the product. Heat transfer vinyl is most commonly used to make apparel--this is what you'll use to make custom t-shirts. You can also heat transfer to materials that aren't cloth, but that's a little advanced for the purpose of this post.
HTV is vinyl that's attached to a shiny piece of plastic, your transfer sheet. You'll be mirroring your image and placing the shiny piece down when you cut it. The shiny piece will be between the actual vinyl and the heat source (that's your iron, easy press, or heat press) during application. It can also be layered (about 3 layers) to make multicolor images, but any special HTV like glitter, holographic, or flocked has to be the top layer.
I honestly don't have a brand preference on HTV; everything I've tried works well as long as you follow manufacturer instructions for cut pressure and heat.
Permanent Vinyl
Permanent vinyl is the vinyl you'll use if you're looking to apply vinyl that will not be removed. It is also sometimes referred to as 651. Popular brands include Oracal 651 and Starcraft HD. (Starcraft HD is my personal favorite.) I've noticed a lot of crafters dislike the Cricut brand permanent vinyl, but I mostly don't purchase it because Starcraft is cheaper and works.
Permanent vinyl is used on drinkware, car decals, signs, and anything else you won't be removing. It can be layered as well to create images with multiple colors. Again, glitter vinyl has to go on top.
Permanent vinyl is not mirrored and cut with the vinyl side up. It is usually on a white backing sheet, kind of like what stickers are on. It is transferred to your piece by applying transfer tape after weeding to the vinyl, detaching the white backing sheet, applying vinyl to the piece, and removing the transfer tape. I'll cover transfer tape next.
Transfer Tape
Transfer tape is the way to move vinyl (with the exception of HTV) from your mat to your project. From Cricut it comes in different grips, but some people use alternatives such as contact paper for this.
Standard grip transfer tape will work for most things. Strong grip is exclusively for things like glitter vinyl that need the extra grip to transfer. Do not use strong grip on regular vinyls, you won't be able to peel it back off to leave your vinyl on the project.
Stencil Vinyl
Stencil vinyl is a type of removable vinyl that works great for projects like etching glass (see my tutorial on that here) and making stencils for paint. The Cricut brand stencil vinyl is what I primarily use, but there is also a cheaper option in Oracal 831. I admit I'm partial to Cricut's stencil vinyl because it has a grid on it which makes it easier for me to determine if I'm applying it straight.
Stencil vinyl has a sticker backing like permanent vinyl and is cut with the stencil vinyl up and typically without mirror, unless you're etching the underside or back of something.
Removable Vinyl
I'll be honest, I don't use removable vinyl really, but this is the type of vinyl that you can actually expect to be able to remove without damaging the item it's stuck to. It's also sometimes labeled 631, and it's commonly used to make window decals/clings. Removable vinyl also has the sticker backing sheet like permanent and stencil vinyl and cuts vinyl up. It sticks pretty well but isn't meant to be outside or things that are handled a lot as it will, of course, come off.