It looks like there are two parts to it. One is the sonar device that goes in the water (the ball) and the other part is the monitor which is hand held or is mounted to the boat. The two devices communicate with each other.
There should be a line attached to the ball so you can retrieve it.
Depending on which model you have will determine whether it is hand held or requires mounting. If there is a mount, the directions should give suggestions on where to place it.
Some of the monitors appear to actually be cell phones and in that case would require downloading an app to communicate with the ball.
If you end up using a cell phone as a monitor you are definitely going to need a waterproof case for it!
I did a search on YouTube for “how to install a fish finder”. There were so many videos to choose from. Some were for specific brands, while others were for specific types of fish. Here’s one. https://m.youtube.com/watch?v=VZiQhBb4woo