Antigen presenting cells include dendritic cells, macrophages and B cells.
All nucleated cells have MHC 1 on their surface. MHC 2 is found mainly on antigen presenting cells.
So processed peptides derived from exogenous sources are displayed on MHC 2 for CD4+ t cells, whilst peptides derived from the cytosol are displayed on MHC 1 for CD8+ t cells.
basically MHC are just proteins that alert the immune system if there is something foreign and dangerous. MHC must have loaded peptide before they are transported to the cell membrane, whether it is self peptide loaded on MHC 1 or foreign peptide.
APC's...well professional APC's like mentioned above are specialised at presenting peptide to naive T cells and activating them if the appropriate signals are received.
tell me if that answers your second question