There's several ways you can do that.
You could make a user-defined waypoint if you wanted to refer to those coordinates by a name. That's what you do on the define pilot waypoint page.
Start by entering the coordinates into the scratchpad, and then line-select them into LL3 (latitude and longitude)
Then, give your point a name (I chose "MYWPT1") and line-select that into LL1 (ident). You can then line-select LL6 to store the waypoint permanently under that name.
You can now refer to this point in your flightplan under that name, here for example by entering it on the LEGS page:
You can also enter the coordinates directly on the LEGS page, bypassing the "define pilot waypoint" stage:
You can tell it's the same waypoint as they are 0.0 nautical miles apart. You can also use the shorthand notation with no minutes, just full degrees.
Finally, you can also use the ICAO notation, 4550N (more information here: http://www.jeppesen.com/download/navdata/navdata_info1.pdf on page 3)
As you can see, there are many ways you can use the default FMS to navigate to a coordinate pair.