I know that if I was there is a simple tense and if I had been there is used in conditional sentences.
But do both mean the same, or, if there is any difference, then what is it?
Can I use if I was there instead of if I had been there in a conditional sentence?
That depends on very precisely just what exactly you mean by “conditional”. There are hundreds if not thousands of valid conditional forms in English. Here are just a few common examples of combinations that may any of them apply in your case, depending on what you actually mean:
If I was there, then so was my dog. I know this because Fido and I always went everywhere together back in those days.
If I was there, then my dog will have been there, too. Like I said, we were inseparable back then.
If I were there, I would say something. But because I'm not going, it's up to you what you'll do in your meeting next week.
If I had been there, I would have said something. But because last week’s meeting is so much water under the bridge, there's nothing to be done about it now.
If you will all please quietly take your seats, we will finally be able to get our meeting started on time.
If you would all please quietly take your seats, maybe we can get our meeting started on time for once.
Please notice how those are all quite different from one another. They all mean different things and are not interchangeable. I've tried to make those differences more obvious by adding more surrounding context to support the intended senses for each. Here below is a correspondingly numbered list of what each of those from the list above "means":
[was + was] = real + real, so this has already happened.
[was + will have been] = real + modal perfect, so this has also already happened; notice especially how that's the kind of will that means the past not the future!
[were + would say] = unreal + modal, so this has not happened but hypothetically might still happen in the future.
[had been + would have said] past perfect + modal perfect, so this did not happen at all because its first part is past perfect, and will not do so in the future; it's completely hypothetical of might-have-beens that never were nor shall ever be.
[will take + will be able to get] = modal + modal periphrastic, this is not the future will but rather the one that means want to.
[would take + can get] = modal + modal, this is the would that means want to just like the previous one with will did, but this time more politely.
See also these closely related answers:
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