Help with new fish finder

[Keepfishing]

I have fished LJ many times without a fishfinder hoping for a YT, but never had any luck.

I tested it out finding structure and did great. I did way better than when I would just drift around hoping for some rockfish.

But I don't know how to use it with yellowtail. Do I just peddle around LJ looking for signs like birds and baitballs, then hope to see big markings on the fishfinder and flyline right there?

Do you use the bottom structure to know where they may be?

Please give me help on signs to look for or what to do when going after them with a fish finder.