The A/F rules are very minimally covered in the rules of Barbaria, so I've copied the full A/F rules here, containing also a few examples to clarify.
Army- Fleet Rules.
a) An A/F may either consist of two units belonging to the same country, or of units of two different countries.
b) An A/F has the same "combat factor" as a single fleet; it may attack, support or be supported.
c) An A/F cannot convoy another army.
d) An Army cannot board an A/F.
e) An A/F can only exist in a sea space - it cannot be ordered to a coastal province as an entity - but it may support some other unit into a coastal province.
f) If an army is ordered to board a fleet, and the A/F is prevented from moving to another sea space the A/F remains intact.
g) If an army is ordered to board a fleet, and the fleet is attacked from another sea space, or if the fleet is ordered to support another unit, the army is considered to have failed to board and it remains in its land province. This is true even if the fleet successfully defends itself against attack.
h) A fleet which lands an army in a coastal province, before making a move, may then support that army to land as its move, or it may move elsewhere. If an army's disembarkation fails, the A/F remains intact and any orders for fleet movement will not be carried out.
i) A fleet may not simultaneously land one army and pick up another.
j) If an A/F is annihilated, then both units are removed from the board.
k) An A/F can be ordered to HOLD. (ie A Lon embarks F Nth, a/F nth Holds)
l) Retreats, Dislodgements and Annihilation. If an A/F is dislodged whilst trying to disembark its A, this move fails and the A and F must retreat together. If an A/F is dislodged and can only retreat to a land space (no suitable sea space being available), the F may retreat but the A is destroyed.
m)Where an A disembarks from the F, and the F then moves away without supporting the A; if the now vacated sea space is then occupied by another unsupported F or A/F, the A disembarkation succeeds; if the second occupation is supported, the disembarkation fails and the A continues with the F.
n) Units of 2 nations may form A/Fs, provided each player involved specifically orders the formation to take place. A combined A/F is always ordered by the owner of the fleet. The army can always be ordered to “get off” by it’s owner, but this only succeeds if the army is ordered to a different destination from the fleet. If the move “get off” does not succeed, the army stands; but if it is dislodged it is disbanded.
o) When a combined (2-Nation) A/F is at sea, the owner of the fleet has the option of disbanding both units in an adjustment phase - scuttling the fleet and the army goes with it.
SO - Now you are completly confused.
CORRECT MOVE EXAMPLES:
A(Lon) E F(ENG); A/F(ENG) - MAO; A(MAO) D Por.
A/F(ENG); A(ENG) D Bre; F(ENG) - NTH.
A/F(ENG); F(ENG) S A(ENG) D Bre.
F(ENG) convoys A(Lon) - Bre.
INCORRECT MOVE EXAMPLE
A(Lon) E F(ENG); F(ENG) S A(Lon) - Bre.