Placement of pronouns

Question

I'm getting confused. This lesson tells us pronouns can go before the conjugated verb  or after the verb, attached to it, except with imperatives it must be the latter. I seem to remember a situation in which they must go before the verb but can't remember what it is.

Answer

Hi Catriona
The position of pronouns varies in Spanish depending on which verbal structure is used. With a conjugated verb the pronouns is placed in front of it and separate, e.g "Ayer te compré un regalo" (Yesterday I bought you a present) But with an imperative it always goes at the end and attached, e.g "Ábrelo" (open it!). This is only for the affirmative commands; if it is a negative command then it is placed in front as other conjugated verbs, e.g "No lo abras" (Don't open it). In the case of gerunds and infinitives they can be placed in front or at the end:
"Quiero comprarlo hoy"= "Lo quiero comprar hoy" or  "Estoy comprándolo" = Lo estoy comprando". 
Have a look at these different lessons for more details:

https://spanish.kwiziq.com/revision/grammar/position-of-direct-and-indirect-object-pronouns-with-infinitivegerund-and-affirmative-commands

https://spanish.kwiziq.com/revision/grammar/position-of-pronouns-with-conjugated-verbs

I hope this helped,
Inma