A part
we use l'll...(=l will) when we've just decided to do something .when we say l'll do something we announce our decision:
for example
Oh,l left door open .l'll go and shut it down.
what would you like to drink.
B part
we often use l'll in these situations.
offering to do something
agreeing to do something
promising to do something
标签：do,use,shall,ll,when,用法,will,something From： https://www.cnblogs.com/andyzheng10/p/17092378.html