For your csv/Excel data, you can use the Add XY Data tool: File menu, Add Data, Add XY Data. After you browse to the file and select it, the tool will default the coordinate system to that of the maps. You probably instead want to override that and choose Geographic Coordinate System, North America, NAD 1983 (or North American 1983 depending on ArcGIS version).
Once the XY layer is created, you can right-click the layer and choose data, export data. In that tool, you can write the data out to a feature class, or a shapefile. There's an option to use the data's coordinate system (NAD 1983) or use the data frame's coordinate system.
To set the data frame's coordinate system to NAD 1983 UTM 18 North, choose projected coordinate system, UTM, NAD 1983. Or in the search box, type in 26918, which should select it for you.
Melita