If you don't already figured out a comfortable way of holding your hook when you do Tunisian crochet, you may wish to view this page:
To get started, crochet a starting chain of any length greater than 2 stitches.
To begin the Tunisian knit stitch, you could work into either the front side or the back side of your starting chain. I usually prefer to work into the back of the starting chain; that way, there will be two loops free to work into across the lower edge in case I want to later add an edging or embellishments to my work. If you take a look at the lower edge of the work in view H, you'll see what I mean by "two loops free".
Views A, B and C demonstrate how it looks if you work into the front of the starting chain.
Views D, E, F, G and H demonstrate how it looks if you work into the back of the starting chain.
To begin, you'll insert your hook into the second chain from your hook. View B shows my crochet hook pointing to the spot where I'd insert my hook if I were going to work into the front of the chain stitch. View E shows my crochet hook pointing to the spot I'd insert my hook when working into the back of the chain stitch. View F shows my crochet hook inserted into the chain stitch.
Next, pull up a loop. (Views C and G.) You're going to leave this loop on your crochet hook for now.
Insert your hook into the next chain stitch and pull up another loop. Repeat that step, inserting your hook into the next chain and pulling up another loop. Keep pulling up loops until you have one loop on your hook corresponding to each chain stitch in your starting chain.
When you're finished with this, your work will somewhat resemble view H in the photo collage.
Don't turn your work; keep the front of the work facing you.
I've seen different terminology applied to this beginning row. It is sometimes called the "base row," and is sometimes referred to as the "foundation row." There may be other names for it as well.
Rows like this where you are drawing up loops can also be called the "forward" or the "forward pass."