你好,by yourself是独立的意思;help yourself是随便吃的意思
by yourself =on your own ,alone
adv.单独地;独立地
[例句]This is a colorful clock that you make by yourself.这是一个你可以自己动手做的彩色钟表。
help yourself
随便吃 ; 自己来 ;请别客气!
1..Help yourself to a clean towel.
请随便拿一条干净毛巾用.
2.Please help yourself to wine.
请随意喝点酒.
3.Can I borrow a pencil?—Yes,help yourself.
我能借用一支铅笔吗?——可以,自己拿吧.