Folks use the paste to fill in the dips in their anatomy which are situated under the barrier/flange.

I have a very deep navel cavity which is a problem for me leak-wise. I used Coloplast's Brava® Ostomy Strip Paste to fill it in until I came up with a better idea. I cut out a small piece which covers my cavity from Convatec's DuoDerm. The stuff is costly to buy but I'll be gone from this world before I can use it all up. It's no mess, no fuss, works beautifully.

As for the two piece system. I use Coloplast's Sensura Mio 2 piece. Perhaps just my preference. I can take the pouch off the flange to shower.

Two piece appliance lets you change the bag instantly when nearing full. No down time at all.
Change the flange every few days at a time of your choice and convenience.

Yes, I can describe the paste, it is called Hollister Ostomy Adapt paste, the Hollister number, is 7906. It comes in a tube and I run a bead of the paste around my stoma before attaching my New Image flange to my skin. Full description below. I also added a picture of my four products that I use.

1. This is the steps I do for each new attachment.
2. I wash my skin with soap and water making sure all soap is off my skin.
3. I then clean it with alcohol swabs usually two to make sure I get all the bacteria off my skin, (I don't touch my stoma with the alcohol) so when putting a new appliance on I don't have any bacteria on my skin that will break down my skin.
4. I then use Hollister Adapt Stoma Powder, I squeeze it around the stoma.
5. I then run a bead of Hollister Ostomy Stoma Paste around my stoma.
6. I then attach the flange to my skin. This way I have the stoma paste as one more defense of attachment so the bag doesn't fall off.
I have done this from the first month I got my colostomy. My surgery was April of 2017 and I have never had any trouble with my skin breaking out getting ulcers under my flange or even a rash.
Good luck and I hope that you never have any problems with you ostomy.

The advantage of a two piece is that I don't have to change my flange that adheres to my skin for every new bag. (which I feel causes the skin to break down with so many changes.) I can rinse the bags out or throw them away but I rinse them often. I get about 7 to 9 days out of each new placement. I don't have to buy so many bags because I do rinse them out and get more days out of them. If I had a one piece I would have to change the whole set up each time I needed to change the bag, which would be for me every day. I have written a long explanation about the paste in a previous note.