How do offerings work?

I'd like to give some offerings to Selene, I feel very drawn towards her. I haven't done it before and I'm a little confused. So after giving an offering do I just take it back after I'm done with the ritual or later? If it's someting I found outside (for example stone, flowers etc) do i just toss it? Feels somehow wrong

What do you feel spiritually happens with the offering? Since the deity/god obviously can't physically take it do you feel like they draw on the energy of the offering or just appreciate the intention? Or something else?