Learn Spanish (Spain): El trípode, lo acabo de montar.

This is called clitic doubling. When you move a direct object (el trípode) to the very front of the sentence to emphasize it as the topic, Spanish requires you to repeat that object with a matching pronoun (lo) before the verb.

Could I attach lo to the end of montar instead?

Yes! Because acabo de montar acts as a single verb structure ending in an infinitive, you can place the pronoun before the conjugated verb (lo acabo de montar) or attach it to the infinitive (acabo de montarlo). Both are perfectly natural and mean the exact same thing.

Why is acabo in the present tense when the English translation uses the present perfect (I've just set)?

The structure acabar de + infinitive is a set phrase used to express something you have just done. Even though the action is completed, Spanish uses the present tense for acabar here. Using the past tense (acabé de) changes the meaning to I finished setting it up, rather than I have just set it up.

Doesn't montar usually mean to ride?

It does! You probably know it from phrases like montar a caballo or montar en bici. However, it is also the standard verb in Spain for to assemble, to put together, or to set up, which applies perfectly to things like a tripod, furniture, or a tent.