Germans do not use the a.m./p.m. system in an official context. When travelling to Germany you will have to become familiar with the 24-hour system, especially when dealing with the official language used on the radio and TV, or at train stations and airports.
Numbers 13 to 24 indicate the hours that English speaking people call p.m., for example
14.21 Uhr = 2:21 p.m.
17.45 Uhr = 5:45 p.m.
20.00 Uhr = 8:00 p.m.
Speaking in person to someone, Germans often use the expressions “morgens” (in the morning), “nachmittags” (in the afternoon) and “abends” (in the evening) to avoid misunderstandings. For example, “Wir kommen um acht Uhr abends an.” (“We will arrive at 8 p.m.”)