Cells can interact with other cells?

Yes. Cells have 'cell receptors' that are used to receive messengers like hormones to communicate. Cell receptors have specific shapes that fit the shape of the messenger that they want to receive. Organs like the pancreas send our these messengers to the cells to order them to do different functions.

it's diluted or concentrated

in a diluted solution, you can add a lot more solute but in concentrated only a little more can be added