Some conjunctions

While

While is usually a subordinating conjunction of time. It can also be used to show contrast.

• Strike while the iron is hot. (Subordinating conjunction of time)
• Thieves broke into the house while they were sleeping. (Subordinating conjunction of time)
• While she is a doctor I am a sweeper. (Subordinating conjunction showing contrast)
• While he leads a luxurious life, his old parents are struggling to make both ends meet.

However

However can be used in two ways. When it is a coordinating conjunction it can stand alone and is generally placed somewhere in the middle of the sentence.

• He is very intelligent. However, he lacks experience.
• The whole class was present. He, however, remained absent.

When however is used as a subordinating conjunction, it takes some adjective or adverb after it.

• However poor he may be, he is not going to beg.

Unless, until and lest

Unless means if not. It shows condition.

• I cannot open the door unless you give me the key. (= If you do not give me the keys, I cannot open the door.)

Until and till can be used both as prepositions and conjunctions. They mean exactly the same.

• Will you please wait here until/till I return?
• I will wait until/till I hear from you.

Lest also shows condition.

• Take exercise regularly lest you should fall ill. (= Take exercise regularly so that you will not fall ill.)

As long as

As long as can refer to a period of time.

• We will have to stay indoors as long as the rain continues.

As long as can also be used to state conditions.

• You can take my camera as long as you use it carefully.