Hi, glad you find Russian fascinating!
Here's the link that might be useful to you: http://www.slovorod.ru/russian-prefixes.html
. It's a list of Russian prefixes with their meanings. As usual, there are exceptions and it's not always deducible from the meaning of the stem and the meaning of the prefix what the compound word means. (You showed examples yourself: although these words seem related very much to me
). So yeah, you got to learn things by heart.
Here's the tip though: when you see a word which you don't know the meaning of but it's composed of a stem and an affix familiar to you, try to deduce what the word could mean, then look it up in the dictionary in case you guessed wrong or couldn't come up with anything. You'll get better the more you practice I think
Oh, and BTW: it's "Добрый день всем!" (dative case).