Hello there. FIrst of all, do you know what version of Moodle you are using? If you are not admin then click on a "Moodle docs for this page" link at the bottom of any page you access as a teacher and look at the number in the URL - 29, 30 or whatever. Then let us know. (If you are admin or can ask the admin then you can find out from Site administration >Notifications)
When you set up an assignment, if you choose a points scale then the assignment will automatically let you mark out of 100 or whatever you want the max grade to be. If you want to add a grade item in the gradebook directly then when you set it up, leave it at the default "value" and you can then add grades of a numerical value.
Perhaps you can give a few more details of where you want to add grades and for what?
As for outcomes, the documentation is here: Outcomes but it might be different depending on what version of Moodle you are using.