Chuck,
Start with the Easier to Read
manual for Sentinel. While this was written for the 436HP & 536HP scanners, at least 90% of the information also applies to the SDS series of scanners. The most notable exceptions would be the enhanced display configuration on the SDS-100/-200, and the filters specific to the SDS series.
There are also a number of videos on
YouTube.
If you are mainly using your location and service type, to monitor using the main database, you may want to use a lower figure for range. You can Avoid (lock out) channels & talkgroups that come up when scanning, but the best way is to create a favorites list based on what you want to hear.
In Sentinel, after you set your location, range, and service types, then go to the Edit drop-down menu.

Click on the option listed as Add Channels in Range.
That will allow you to create a Favorites list based on your current settings. It would be essentially the same as hat you are hearing using only the main database, along with location and service types.
Once that is created in Sentinel, then you can edit the list to remove, or lock out, what is not of interest. Once you've tweaked it to your satisfaction, then you can use Sentinel to write it to your scanner & listen.
You can also create, or add to an Existing Favorites list by appending systems from the main database. In Sentinel, click on the
+(plus) sign by the database to expand out the lists of states. Then, click on your state and find your county.

You can click on each listing to see what it contains.