Dave is right. The point of the plow has to dig in. If the ground is really hard, it may be hard to get penetration. I'd suggest adjusting the toplink shorter so the tip of the plow can break into the soil. Once you get the plow started, you'll find subsequent rows should be easier. If, after starting the row, the plow digs in too much, lengthen that toplink a bit to keep the plow at a shallower level. Also adjust your sidelink so that the soil curls over and a good furrow is left on the outside for the next row. Place your right side wheels down into that furrow on successive rows.
Jim is correct.
In addition..
Set up your plow with it and the tractor setting on level ground.
Depending on your wheel width you may have to adjust your plow to the right and lock it there with your side sway pins.
This will effect the level, so check that again.
After you make your first pass you will need to adjust again with your right wheel sitting in the furrow especially if the plow has
multiple points.
If you have a DRAFT CONTROL lever on your tractor that is what you will use to control the depth while plowing and keep your
drive wheels from slipping. Set your raise/lower lever to the depth you want while making the first pass and leave it alone after that.
You may have a little adjustable stop that you can set and screw down to keep you from the urge to lower the plow further with that lever.
The draft control lever doesn't hold the plow down as such, but it adjusts how much resistance it takes to allow the plow to lift a little bit
to keep it from going too deep.
When you get to the end of the row use the draft control lever to lift the plow up away from the ground so you can turn and go to the other side
of your garden for a pass along that edge.
When you get it all plowed in between the sides you might want to go across the ends once to even them up.
It takes some practice and experience to get it right and a small garden doesn't give much of that for a few years.
You may notice the cross shaft on the plow where your lower links go on is higher on one side than the other.
If yours is, you may have to adjust the length of one of your tractor side link rods as well.
If you have a disc wheel in front of each plow point adjust them to cut the grass ahead of the plow if this
is a new spot.
Depending on your soil, you will need to learn when it is too wet or likewise too dry to plow.
When you get done the plow surface should be shiny smooth.
Smear some grease or oil on it to keep it from rusting before the next use.