Using one of those tuners is very simple. (mostly)

Assuming you are using ladder or window line,(not only a good
assumption, but a good idea) put up as much wire as high as you can.

The "mostly" part is that you don't want the wires to be 1/4 wavelength
total on any of the bands you are going to operate. I think the MFJ
manuals point out some lengths you don't want to use.

All this is to say that if you can put say 96 feet of wire in the air,
that is what you put up. Such an antenna will work a treat on 40 and up,
decently on 80 meters, and almost so-so on 160.

You are ready. Get a couple buds, your slingshot or favorite method of
launching fishing line into the air, and put up that dipole. Run the
window line to the house, avoiding running it too near to metal objects,
say keep it around 4 inches away. Connect it to the balanced line input
on the tuner, go coax to the rig, and there you have it. Make sure you
do the grounding thing correctly, but that's another subject.
======================
Whatever the length of the dipole ,ensure the the length of 1 half of
the dipole + the length of the 'window feeder' is approx 1 quarter
wavelength of 160m . This will result is a reasonably low impedance at
the matching unit (tuner) , which that unit will happily accept.

Frank GM0CSZ / KN6WH