Tailoring is a trade skill. You are allowed to learn two (2) trade skills. You can always unlearn the tradeskill by talking to the trade skill trainer. In this way you can learn another trade skill if you like.
Then you need to learn recipes. You can buy them from Annie Pattern in Ipcus or Patten in Lynderyn. Some recipes are monster drops, this is indicated in the 5th row. Click on the name in this wiki to find you where you can get them.
Double click the recipe and you will learn them. It will state the ingredients, but you can find them later in this wiki as well (see #Tailoring Patterns).
Buy/get the ingredients. Some can be bought from Snobby Leoda Pattern in Ipcus or Nellie in Lynderyn, but some are monster drops. Click on the ingredients in this wiki to find out where you can get them.
Open your combine bag
Place the ingredients (not the recipe!) in this combine bag. You can place stacks of items (CTRL+drag) for easy manufacturing of a number of items. In this example I used Tailoring Ingredients.
Press the Create Button and your item will be created. Drag the item to you inventory. .
NB: if you placed stacks of ingredients for many creations, you need to drag the created item to your inventory after each creation. Otherwise your ingredients do not match the recipe (since there is an extra item) and nothing will be created.
NB: if you placed the correct ingredients but the item is not created, then maybe you forgot to learn the skill or the recipes. Otherwise maybe you forgot to remove the created item from the session before.