So ive always had my bitcoin in my hardware wallet. Now there are 2 options: Legacy and Segwit. Whats the actual difference ?

1. Can i transfer my btc from Legacy to Segwit as a normal BTC transfer ?
2a. Does it make a different where i hold my bitcoins ?
2b. Do they use the same hashpower ?
3. Considering segwit was activated, why my BTCs are not automatically on the Segwit chain (are there actually 2 chains ?)
4. Whats my play ?

i know that my questions are very much beginner questions, and some os my premises might be wrong. Please educate me