Your transducer will point toward the bottom but not necessarily at a perfect angle. On my boat I can see the lure if I put it on the starboard side near the back of the boat. You can find your sweet spot with some searching at a bottom depth of 30-40 feet. Use a spoon for best results.
Yes when you see "fish" they are really there. Now what does a fish look like? Many of these targets are fish but not all. If most of the targets are identifiable then try to fish for them. If not mark the spot and graph some more and then come back to the spot and look again..
drop your spoon under transom of boat 30 foot down, adjust angle transducer until you see it on the screen, also may have to play with sensitivity , increase until you get random noise on screen then back off until clears up. basic setup, must be able to see your jig or your using your sonar to its capacity.
I can see my lure drop to the bottom on my front finder, and I'm sure it would show on the back one as well. When drop shotting you will see a double line dropping down, one line is the sinker and the second line is the lure.