From ArcMap help: To add a table of x,y coordinates to your map, globe, or scene, the table must contain two fields: one for the x-coordinate and one for the y-coordinate. The values in the fields may represent any coordinate system and units such as latitude and longitude or meters.
If you have heard UTM does not work, that is because UTM units often stored in one text field with zone, x, and y values. That would require using some other way to create points, such Convert Coordinate Notation.
It sounds like it did work for you if you got locations; you skipped a step in which you tell it you are using UTM and which zone. In ArcMap 10.6 this is done by using the Edit button in the Description/Input Coordinates box. It is not clear what version you are using.