Marking a Line
With the shower pan installed and the backing board properly cleaned, you will then need to make a mark that is equivalent to the height of a tile plus a half-inch more. Then, transfer this line all the way around the shower, as this will give you a lip over the edge of the tile pan.
Applying the Thinset
Before starting with the thinset, or the tile adhesive, you need to dampen the cement board with a sponge, ensuring that the adhesive does not dry out too quickly. Use the trowel to spread on some thinset and use the notched trowel to give it texture for the tile to adhere to. If you press it on with a slight twist, it will provide good coverage in the grooves on the back of the tile and improve the stick.
Gapping the Tiles
You can finish the bottom row in the same way, using tile spacers to ensure that the gaps between the tiles are even and not too large. Keep in mind that these gaps will later be filled with grout. So, if they are too large, it will look odd.
Letting it Dry
It is a good idea to let the bottom row dry for around 24 hours. This way, the tile will not slide when the upper tiles are applied. In addition, they will give the higher rows of tiles a good base.
Moving Up
You can now continue to the top of the shower by adding additional rows of tiles. When you reach the top, if the tiles do not fit exactly, you will need to cut them to size. Tiles around any fittings, like pipes, showerheads or controls, will need to be clipped into shape and filed smooth.
Grouting the Tiles
After the tiles have set for 48 hours, they can be grouted. Either mix the grout yourself or use the premixed version. A sponge float can be used to smooth it into the gaps left between the tiles. Thanks to the spacers, these should be all relatively small and even. Check on the back of the grout bag to see how long you need to leave it in place. Then, wipe the excess away with a damp sponge until the tiles are clear and there is no residue remaining. The grout will need 24-48 hours to dry completely before you can apply the final sealing.
As a final note, you might want to use plastic sheeting or similar to protect the shower pan from any drips of grout or, worse, an accidentally dropped tile, which could crack or mark it. If you don't feel confident taking on this job yourself, perhaps taking a tiling course might help. Not only will you learn the basics of tiling, you can learn some advanced techniques as well.