For sure a Hayward DE filter. It is a requirement that you "crack" it open at least a couple of times a year.. And since you just bought the place, and have no idea how long it has been since the last time it was cleaned, I'd do it sooner than later.
Basically, your filter has grids that hold a powder called Diatomaceous Earth (DE). The valve in front of your filter allows you to backwash most, but not all, of the used and dirty DE out of the filter. You then have to add more DE. But since backwashing does not get all the dirty DE out, after backwashing 3 or 4 times, the filter needs to be taken completely apart and cleaned.
You can check out how to do this in pool school or on U-tube. My suggestion is that you hire your local pool store to come out and do this the first time. Just watch what they do and then you can do it in the future. The first time I did this, it took me an hour to get it back together.. Now it takes about 10 minutes. It is very easy once you have done it a couple of times.
Good Luck with your new pool.
Jim R.