Problems With Thunderbird

[diddlydo]

Against my better judgement but following advice on here, I downloaded Thunderbird to stay logged in to email. However, although it sends and receives emails I can't see any way of importing all my email folders from BT Yahoo. Plus, when I send a message using Thunderbird it doesn't show as a sent message in my BT Yahoo sent box. This is useless for me but I feel I must be doing something wrong as it's so highly recommended. Please help!