Mito's merge functionality can be used to combine datasets together horizontally. Merge looks for matches between the key column of the first sheet and the key column of the second sheet, and then combines those matches into a single row.
To merge datasets together, click on the merge icon in the Mito toolbar and then configure the merge task pane by:
First, selecting the two Mito sheets that you want to merge together.
Second, choosing the Merge Keys to merge the datasets together on.
Using the columns toggles to determine which columns to keep from the previous two sheets.