insert - reference geometry - plane.
But perhaps it is better to "explore" all the commands and find out yourself.
Also the use of HELP can be very helpful.
But if it is very important to "create new things and designs"....perhaps it is wise to get professional help (school, course, or buy a solidworks book)
If you do not know how to add a new plane (one of the basics), than you will get into more problems.......