一边 (yìbiān) goes before two actions to show that one person is doing both at the same time, like eating while watching TV. It is the everyday way to say "while" or "as" in Chinese.
Subject + 一边 + action 1, 一边 + action 2.
Put 一边 directly before each verb. Both actions are done by the same person and happen at the same time. The comma in the middle is optional. In English the order often changes: 我一边吃饭，一边看电视 is "I watch TV while I eat".
The most common mistake is to put the subject after 一边, as in 一边我吃饭. The subject goes before the first 一边, and you don't repeat it after the second one. Also remember the second 一边: 我一边吃饭，看电视 is not complete.
To tell someone not to do two things at once, put 别 or 不要 before the first 一边.
In speech you will also hear 边……边, mostly with short, one-syllable verbs. It means the same thing.
一边……一边 is only for actions. To say something has two qualities, such as big and sweet, use 又……又 instead: 又大又甜, not 一边大一边甜.
Practise this grammar point on paper: 16 exercises using only HSK 3 words, with an answer key on a separate page. Free to print and copy for your class.
Every example on this page uses only words up to HSK 3. Paste your own sentences into the level checker to see which words, if any, are above your level.