1to be at home
2(at a workplace) to be in (as opposed to being away on official business 出差)
3(Buddhism etc) to remain a layman (as opposed to becoming a monk or a nun 出家)
Examples
wǒ我ér zi儿子bú不zài jiā在家，tā他zài在xué xiào学校。
我儿子不在家，他在学校。
My son is not at home, he is at school.
晚上六点到上午八点在家。
I'm at home from six o'clock in the evening to eight o'clock in the morning.
明天下午，我爸爸妈妈都在家。
Tomorrow evening, both my dad and my mom are at home.