Cell

sky130_fd_sc_hd__tapvpwrvgnd_1.mag

would be better option for tap as VPWR and VGND are already connected in it.

For the part where you want to select a cell, in magic you can also 1) go to "Options" -> "Library manager", there you'll find the whole list of libraries without having to browse through a bunch of paths. Or 2) if you know the cell you can use the TCL console and type (replace with the cellname you want)

getcell sky130_fd_sc_hd__inv_1

Updated the doc with these tips