“他们自己学用英语” 可以用英语表达为 "they teach themselves Engpsh" 或 "they learn Engpsh on their own".

这个短语的来源是由两个独立的词组组成："teach oneself" 和 "learn on one's own".

"Teach oneself" 意思是自学，即自己学习某项技能或知识而不需要他人指导。

"Learn on one's own" 也意味着自学，表示自己独立学习某项技能或知识而不依赖于他人的帮助。

下面是一些例句：

"I taught myself how to play the piano." (我自学了如何弹钢琴。)
"She learned to speak Spanish on her own." (她自学了西班牙语。)
"He's been teaching himself coding for the past year." (他过去一年一直在自学编程。)
"I've been learning French on my own using onpne resources." (我一直在使用网络资源自学法语。)