This forum for communication removes the visual barriers that hinder some students from expressing themselves. (Para.3)
Meaning: As a place for communication, the online method doesn't require people to see each other personally. So some students won't feel it difficult to express their ideas.
visual: a. gained by or connected with seeing
Visual knowledge of a place of battle helps a general to plan his attack. 親臨戰場對將軍制定攻擊計劃很有幫助。
The visual arts are painting and dancing, etc. as opposed to music and literature. 視覺藝術是繪畫，舞蹈等，與音樂和文學相對。
barrier: n. something placed in the way in order to prevent or control the movement of people or things
The police put up barriers to control the crowd. 警察搭起路障對人群加以控制。
The color of one's skin shouldn't be a barrier to success. 膚色不應該成為成功的障礙。
hinder: vt. prevent sb. from doing sth.; prevent sth. from happening
I'm sorry that some business hindered my answering your letter. 很抱歉，由于忙于一些事務，未能回信。
Don't talk to me now; you will hinder me. 現在不要和我講，那樣會妨礙我的。