A polite/respectful way to refer to one's father (or someone else's), commonly used in conversation.
お父さん、今日は早く帰ってきてくれてありがとう。
Dad, thank you for coming home early today.
明日、お父さんに仕事のことで相談します。
I'll consult my father about work tomorrow.
お父さんは釣りが好きで、毎週末出かける。
My dad likes fishing and goes out every weekend.
Can be used politely to refer to someone's husband in certain contexts.
彼女のお父さん（＝夫）は会社員です。
Her husband is an office worker.
来週、お父さんに会わせてほしいと言われた。
I was asked to meet her husband next week.
In familiar or colloquial speech it can be used to address an older man as 'you' (or sometimes to mean 'he'), a dialectal/less common usage.
お父さん、そんなこと言うなよ（年長の男性に対して砕けた言い方）。
Hey old man, don't say that (colloquial to an older man).
あの人？ああ、お父さんは近所でよく見かけるよ。（文脈により“彼”の意味）
That person? Oh, I often see him around the neighborhood.