Amicably is how you do something when you keep it friendly and do not quarrel. If two people settle a bill amicably, or part amicably, they handle it in a civil way — no shouting, no long feud. It has the same slightly formal, “we kept it polite” feeling as amicable. You will see it with verbs like settle, agree, discuss, divorce, and part. In ordinary chat people more often say “in a friendly way” or “without a fight.”