Learn Dutch: Is er iemand thuis? - Is there someone home?

To ask a yes/no question in Dutch, you put the verb first. A normal statement would be Er is iemand thuis (There is someone home). By swapping the verb (is) and the placeholder subject (er), it becomes the question Is er iemand thuis?.

Could I say 'Is daar iemand thuis?' instead?

Not if you mean 'Is there someone home?'. In English, you use 'there' both for pointing at a place ('over there') and for stating existence ('there is'). In Dutch, daar is only used for a specific location. When saying 'there is' or 'is there', you must use the existential word er.

What is the difference between 'thuis' and 'huis'?

Een huis is the physical building (a house). Thuis is an adverb that means 'at home'. Since you are asking if someone is currently at their residence rather than talking about a building, you use thuis.

Does 'iemand' translate to 'someone' or 'anyone'?

It translates to both! Dutch doesn't make a strict distinction between 'someone' and 'anyone' the way English does. In a question like this, iemand works perfectly for either meaning.