I have little to no experience with the construction set and I wanted to know what is the best way to take an already existing item (for example the black hood) and give it an enchantment that does not appear in the game (for example drain magicka 500 points)? Once that item is made in the construction set how do I get that item, like console command it, for example? Thank you.

Go to TES Alliance and go through their http://tesalliance.org/forums/index.php?/forum/12-construction-set-basics/ tutorial. That will teach you everything you need to know in a reasonably short amount of time.

You may also want to peruse the http://cs.elderscrolls.com/constwiki/index.php/A_beginner%27s_guide%2C_lesson_1_-_The_Construction_Set_Primer at the CS Wiki.