Start by teaching your dog by issuing command when training him.
Commands are special words that you repeat over and over to condition him to obey.
Although there are certain command words that most trainers teach, in theory you could use any word you want to designate a command. 
The most important thing is consistency. You must always use the same word for the same command. Mixing command words up will only confuse your dog and make training him more difficult if not outright impossible. The tone and pitch of your voice is also important. It must be commanding.

4 most important commands

The first 2 are conditioning commands that you use in combination with action commands.

No

As the word implies, no is used whenever you want your dog to stop whatever he is doing. For instance if he urinates on the floor instead of going to his crate to pee saying no in a stern tone of voice gives him the message that what he did is unacceptable. 
The key thing to remember with dogs is that your tone of voice is extremely important when commanding your dog. This is because dogs are very influenced by voice tone and body language.

Good Dog

On the flipside saying “good dog”, lets your dog know that you approve of what they just did. When you say this you should combine it with a physical gesture praising your dog for a job well done. This one should come naturally to most of us but it is important to know how to use it in combination with other commands so you can positively condition your dog to obey you.

Stay

Getting your dog to stay in one place can be a challenge. That's where this command fits in. Sit your dog down and with a stern tone and command your dog to “stay”. If he doesn't listen, say “no” and start again. The key is repetition and consistency. If you start while he's a puppy it shouldn't take too long.

Sit