to show that something is very important or worth giving attention to

[ + question word ] I'd just like to emphasize how important it is for people to learn foreign languages. 我只是想强调一下学习外语的重要性。

[ + that ] He emphasized that all the people taking part in the research were volunteers. 他着重指出所有参加这项研究的人都是志愿者。

You can use italics or capitals to emphasize a word in a piece of writing. 你可以用斜体或者大写来强调文章中的某个词。

to make something more obvious

A good way to emphasize your interest in the job is to write a follow-up email after the interview.