HAD83
To me, understanding the SI display is a lot like looking at an Xray.
The information is there, you just have to know what your looking at.
Some fish are easy to see, some are not.
Another variable is where they are located in relation to the transducer,
ie, high/low in water column, near/far from the boat, in/near cover, if they were parallel/perpendicular to the SI beam .... it goes on.
The fish normally show as white marks. Sometimes in a ball or scattered group or individual fish.
It takes time and experience and then you end up taking an educated guess until you catch one.
Here's a link to good HB site that is primarily fishing orientated. Don't miss the seminar in the lower right corner. It's a hour long.
Your going to do fine.
http://www.jasonhalfenoutdoors.com/HumminbirdIndex.html Mike