Domestic Hot Water Piping

Hello Everyone,

I am working on this building which has a combi steam boiler producing domestic hot water as well as steam for space heating. Now, I came across this domestic piping arrangement shown in the pics below. I am not able to understand the piping arrangement going into the storage tank.

The pipe coming from the boiler connects to the top of the storage tank. Also, there's one more pipe coming off the storage tank connecting to the return side of the domestic hot water pipe. I drawn a pipe layout for better understanding. I have a few questions below:

1. How does this piping arrangement works?

2. Is the flow of water coming in and out of the storage tank correct in the piping layout that I drew?

3. There's a gas line connecting to the storage tank via manifold (can be seen in the pics)

Thank you.