'Iar' is a conjunction and it has the same meaning as our 'and'. Yet, it can't always replace 'and'. There was a language learner who used to ask me why he couldn't always use 'iar', instead of 'şi' and I couldn't give him the exact answer. But here it is how I think of 'iar'. When using complex sentences, and you build a structure that is based on an antithesis, 'iar' is required, meaning something like as to/ as for. I'll give you an example: Cats are very enjoyable pets. As for fish, they are less fun. Pisicile sunt animale de companie foarte drăguţe, iar peştii sunt mai puţin distractivi. Also, we use 'iar' when we get together two phrases: El este Ion, iar ea este Maria. We never use 'iar' in this situation: Îmi plac florile, iar pomii, iar cerul. We say: Îmi plac florile, pomii şi cerul.

It has several meanings, depending on the context: and/again/while. Can you be more specific?