Article: You'll need thin set mortar to lay your tiles. While you should always go by the manufacturer's instructions, a general rule of thumb is to start with the powder in a bucket and just add water slowly and mix until the consistency of the mortar becomes like peanut butter. You should also allow it to "slake" after you first mix it up. This means you allow it to rest for 10-15 minutes and then stir it up again. Now it is ready to use. Working in a roughly 2x3' area, use a tiling trowel to apply the mortar. Hold the notched trowel at a shallow angle against the wall, so that the notches on one of its long sides dig grooves into the mortar. Use long, sweeping motions to apply the mortar. The direction of the grooves doesn’t matter but the lines should all be roughly parallel.  Your trowel size will depend on the size and type of tile you're using. For the average small wall tiles which are currently popular, you will want to use a 1x4" square notch trowel. Test a tile to make sure the mortar is mixed and spread correctly. Mortar a small spot and then place a tile. Pull the tile up and look at the pattern that is create on the back. If you see clear lines, then the mortar is too dry. If you see goopy mounds then the mortar is too wet. With the mortar ready to go, you can start placing your tiles. Just  twist them into place, sticking to the small area that you prepared for yourself. Place your spacers between each tile as you go. These are usually cross shaped and placed at the corners but if you have unusual tiles you may have to improvise, such as by placing only one arm between tiles and letting the rest of the spacer stick out.  If the mortar rises up between the tiles as you place them, the bed is too thick and you will need a smaller trowel. Check the tiles for level as you go. This is when a laser level can really come in handy.

What is a summary?
Mix the mortar. Spread the mortar. Place your tiles on the wall.