So if you have 100 XEM in XEM wallet, you will receive 100 XYM in XYM wallet. In total you will have 100 XEM and 100 XYM. Two different blockchains and tokens.
Sure?
Snapshot is the term for when we take a "picture" and record everyone's XEM balance across the NEM blockchain. This is then used to populate the new SYMBOL tokens in the new SYMBOL blockchain. One SYMBOL token for every 1 XEM token at the time of snapshot will be put on the new SYMBOL platform blockchain.
https://support.nem.help/hc/en-us/articles/360034476171-BASIC