how to colonize

Fly into them with a colony ship.

i mean how do you send a specific ship into a specific planet and then make it colonize cuz i can't send a ship int o the planet it goes right aroung it

First, you must be using a ship with the Colony Module - the core Colony Ship or one you have designed which includes a Colony Module.

Bring the ship out of orbit and select it with a left-click, then right-click on the planet you wish to colonize.

The planet must not already be owned by another civ, of course, and it must be a habitible planet. If you are using DA, you must also have the techs to colonize that type of planet.

When the ship reaches the planet it will automatically colonize it, and you will receive a message and be put into the planet screen to start building.

In order for a ship to colonize a planet, it must have a Colony module installed. The Colony ship that you get automatically at the start of the game has one. Simply select the ship, and click on the planet you wish to colonize. You should note that not all planets are suitable for colonization, and your colony ships will not land on those that will not support life. The planets all have a number associated with them, which is their desirablity. If the number is 0, you can't colonize that planet.