First you need to learn numbers. When you are confident with numbers you can easily say the time.
9:15 – девять пятнадцать (nine fifteen)
12:30 – двенадцать тридцать
11:45 – одиннадцать сорок пять
15:00 – пятнадцать ноль ноль
20:20 – двадцать двадцать
You may also use the word «час» (o’clock). But there is one tricky thing you should remember when you use this word – it changes its ending. The ending depends on the number it’s following. If there is 1, the word stays the same (1 час), if there is 2, 3 or 4, the ending is -а (2 часа). For numbers 5 and bigger the ending is -ов (5 часов).
But after the 20 the ending depends on the last number.
For example:
Сейчас 21 час – it is 9 pm.
Сейчас 22 часа – it is 22 o’clock (10 pm).
Я жду 25 часов – I have been waiting for 25 hours.
Some useful phrases about time
a.m = утра
p.m = вечера
1. Сколько времени? – What time is it?
2. Во сколько у нас урок? – At what time do we have a lesson?
3. Я встаю в 6 (шесть) часов утра. – I wake up at 6 a.m.
4. Я ужинаю в 6 часов вечера. – I have dinner at 6 p.m.