This could be the stupidest question I have ever asked here (??) but...
I realise that apart from Ground and Tower I am really not very sure about what the other facilities are - Multicom, Unicom, FSS, Center... How do I know which facility I am currently tuned to? I found in the pdf a description of the key actions for each facility but not what the facilities are, as it were, and when they are active. Changing from one to another at will (in flight, say cruise) is not possible, logically?
I realised that my flight plan was taking me to the wrong airport just now, but had no idea how to request a change of destination...
Could someone kindly point me to an explanation? Thank you!