Learn Italian: Lavoro qui da due anni. - I have been working here for two years.

In Italian, when an action started in the past and is still happening right now, you use the present tense. Because you are still working there today, you use the present tense lavoro, whereas English requires the present perfect continuous.

Does da mean 'for' here? I learned it means 'from'.

You are right that da often means 'from'. However, when talking about time, da is used to express how long an ongoing action has been happening. In this context, it translates to the English 'for' (a duration) or 'since' (a starting point).

Could I use per instead of da in this sentence to say 'for two years'?

Not if you still work there! You use per only when a duration of time is completely finished in the past. If you said Ho lavorato qui per due anni (I worked here for two years), it would mean you no longer work there. Because the action is still ongoing, you must use da.

How do I know if da translates to 'for' or 'since'?

It depends on what follows it. Because due anni (two years) is a length of time, it translates to 'for'. If it were followed by a specific starting point in time, like a year or a month, it would mean 'since'. For example, dal 2021 means 'since 2021'.