The Humminbird and Lowrance transducers with conflict with each other, but I think there is a connector you can buy to make them use a single transducer and "talk to each other". I haven't actually seen it work, but I saw one the other day in a box. Those should both have down imaging hence the DI in the Lowrance and the 898 is a DI unit. Depending on which 898 it actually is, it may have side imaging. There should be more to the name, it should have HD SI at the end. The Lowrance does not have side imaging I don't think.
As for using them, there is a guide on Fork that is supposed to be really good at teaching sonar. You can also google "you tube sonar fish" and will find tons of informative information. The videos will get you started and then just put in some time cruising around a local lake. Then go back and watch them again. For some samples look in the Crappie section of this forum and there is a post at the very beginning that says "Crappie Graphs". Look at those, they are very informative for what you are looking for irrelevant of the fish. Also, remember that most of those pics are from a computer and the resolution on your graph will not be quite the same but it should give you an idea of what you are looking at.