Ferry from Sorento to Capri

Is it easy to catch the ferry from Sorento to Capri

Yes.
https://www.capri.com/en/getting-here
https://www.sorrentoinsider.com/en/t/sorrento/capri

what recommended points of interest on island?

That depends on your interests. We enjoyed exploring the island on foot to some of the spots which were of interest to us. Those were:
Villa Jovis:
https://www.capri.com/en/e/the-villas-of-tiberius

Piazzolungo/Natural Arch
https://www.capri.com/en/e/pizzolungo-2

Gardens of Augustus
https://www.capri.com/en/s/augustus-gardens-via-krupp

Charterhouse of San Giacomo
https://www.capri.com/en/s/the-charterhouse-of-st-giacomo

Short bus ride up to Anacapri for a walkabout of the village and chairlift up Mt Solaro
https://www.capri.com/en/s/mount-solaro-cetrella

And, of course a walkabout of Capri village, some browsing of local shops in Anacapri, and some kickback time with adult beverages to just enjoy the view. :O). We had 2 nights/1.5 days on the island so if you are day tripping, your time will be more limited. What did not appeal to either of us was the Blue Grotto: enough reviews were negative enough about the price value and experience in general that we didn't feel like we'd missed anything by skipping it. Villa San Michelle wasn't high on our list either but others have felt differently, as it often goes (and should go) with personal-interest itineraries.

We didn't take any organized tours 'cuz we did fine with a map and other materials picked up locally + the website.
https://www.capri.com

Returning to Sorrento, best to plan to the take the 2nd to last ferry of the day, unless you want to leave earlier. That way if you miss it, you still have that last boat to get you back.