Remember that conjunctions are phrases that help us join two clauses or ideas. In the case of conditional conjunctions there is a conditional clause (what has to happen/happened/will happen) and a result (which only happens/happened/will happen if the condition is fulfilled).

Conditional conjuctions can be used in the place of if/if not. The most frequent are: even if, unless, whether, as long as, provided / providing that.

UNLESS

Unless means: if...not. Like if, it is followed by a present tense, a past tense or a past perfect (never by 'would'). It is used instead of if + not in conditional sentences of all types:

You won't get in to see the show, if you don't have reserved seats. OR:
Unless you have reserved seats, you won't get in to see the show

I wouldn't eat that food unless I was really hungry (2^nd conditional)

I wouldn't have phoned him unless he had asked me to (3^rd conditional)

However, we cannot use unless for questions: What will you do if you don't pass those exams?

As long as / provided / on condition that = but only if

We can use these alternatives to IF if we want to emphasize the conditions that surround the action: One thing will happen as long as another one happens

Providing, provided and on condition that are more formal than IF:

We will lend you the money on condition that it is repaid within 12 months.
We will lend you the money provided/providing that you can repay it within 12 months.
You can borrow my car as long as you return it on Sunday.

Even if = to emphasize if

I would have a good time even if it rained 

WHETHER

You can generally use if or whether when you are reporting yes/no questions. It doesn't matter which you choose:

Can you feed the cat for me while I'm away? →→

She wanted to know whether/if I could feed the cat for her while she was away.

However, after prepositions, before to-infintives, in whether...or... constructions and whenever we start a sentence with the conjuntion, we have to use whether:

Whether I'll get there in time for my exam, I don't know.
I can't decide whether to buy some new clothes now or wait until the sales..
There was a lot of discussion about whether Sam should get a motorbike or not.
I'm going to spend all my money on a new car whether you like it or not!