There are a number of different ways to create the long tail cast-on. The method shown here in this video is the most standard method for creating the cast-on.
The only difficulty knitters have with this cast-on is figuring out how long to leave the tail. A usefully little knitting hack if you have problems with this is to use the second end of your yarn skein instead of a tail so you can’t run out!

Here’s a video of it in action: