Do you mean copy the contents of one cell and then paste it to multiple cells horizontally?
Tap once to select the cell. Tap again to get the pop up menu. If you do this too close together, like double click speed, you'll get the cell editor instead of the menu. Choose copy.
Now tap on the first cell you want the data copied to. Drag the handles to include the cells you want. This can be horizontally, verticaly, or both. Tap the selection, then choose Paste from the pop-up menu.
You can also get the menu by Tap, Tap-hold (at double click speed), but if you release your hold too soon you'll get the cell editor. You have to hold for about a second after the menu pops up, or slide you finger off the cell to avoid that.
Now, if you were trying to get text in a single sell to extend through multiple cells, select the cell, select the info icon, Cells, and turn off Wrap Text in Cell.
When you do this the text will extend over any empty cells to the right of it. If those cells have contents, or are selected, the text will not cover them
Another way Excel does this is by joining cells. As far as I can tell (and I searched the help page) Numbers does not have this option.
If you just wanted to create a multi-cell lable in the middle of the spreadsheet, you could use a shape. I found that the square shape snaps to the cells fairly well (most of the time), and you can change it's color and the text in it.
Thank you for another excuse to play arround with Numbers, just to see what I can do. I enjoy playing arround with it, but because I don't have any real use cases for myself, I don't ask myself any good questions.