Hi,there're two ways to say the time in British English:
-Saying hour to minute:this's used in formal context and easy to remember.
examples: 6:45 (six forty-five), 12:06 (twelve oh six),...
-Saying minute to hour:this is common way--from the 1st minute to the 30th minute we use "past",from the 31st minute to the 59th minute we use "to".
Examples: 6:45 (fifteen minutes to seven), 12:06 (six minutes past twelve),...
*Besides,we use some other ways to say,like:
`15 minutes past = a quarter past (Ex: 8:15 = a quater past eight)
`15 minutes to = a quarter to (6:45 = a quater to seven)
`30 minutes past = half past (ex:4:30= half past four)
-"o'clock" used to specify the hour(ex:7:00=seven o'clock)
*We use "a.m=ante meridiem" and "p.m=post meridiem" in the formal/daily contexts.
Example:7:00=7 a.m,14:00=2 p.m,...
And we don't often use "a.m,p.m" with "past/to".
**Whereas,American English has some differences:
-They use not only "past" but also"after" (ex:3:10=ten after/past three),but "after" can't replace "half" in "half past".
-Besides "to",American often use "before/of/till",too.(ex: 2:50=ten to/before/of/till three)
~~~~~~~~Do they help?:)