Letter O

[Konnova]

Hello again) Maybe this question is very simple, but could you tell me the difference between the pronunciation of letter "O" sometimes it occurs like "ou" sometimes like "eu". Is it American and British English?

[Cerberus™]

Yes, in general ou is American and eu British, leaving aside the many subtle and not so subtle differences within either group of dialects. (I assume you are talking about phonetic notation, not the actual, so written ou or eu.)