The bad news is that when a trial balance does not balance, there is not any way for anyone to know what is wrong without seeing all the work that went into making it. For instance, if you've had to do journal entries or t accounts or ledgers yourself, and then do a trial balance when you're done, I'd have to see every bit of that work to know what was wrong. Mostly, because I don't know any more than you do. I simply have more experienced at tracking down errors... But still need the information to track it down.
I can give you some hints on what to try. The obvious: re-add the columns and make sure it agrees with what you got the first time. Also be sure to write these totals down so you can work with them. Then subtract the two columns to see what the difference is. Look for that number anywhere in your work. You may have just missed putting one account in the trial balance or something. Then divide this difference in two and look for that number too. When something ends up on the wrong side, the error will double itself. For instance, if you put a $50 debit into the credit column, the two columns will actually be off by $100. So if you take the $100 and divide it in two, you'll have the $50. Then you can see if you can find that.
You can also do things like taking that difference and dividing by 9. If it's evenly divisable (i.e. A whole number answer), then it might be you turned two numbers around. I.e. 750 instead of 570. I don't personally bother with this one, simply because it only might be you turned two numbers around, and because you still don't know where the error is and have to look anyway.
From there, work backwards. The last thing was copying the numbers to the trial balance, so check them all to make sure they're correct. (Check carefully. Easy to miss things.) If you've had to do t accounts or ledger accounts, re-check your math to make sure the balances are correct. Etc.
If you'd like, you can post your trial balance, and if it's just a matter of something being on the wrong debit/credit side, someone can spot that. But if there's other types of errors, we can't find them without the rest of the work.
As for filling in blanks... Are you meaning that you have a bunch of account balances with a missing number? I.e. You have a balance for every account except for, say, cash? And then you have to find cash? That would be a matter of making the trial balance, totaling both sides, and the difference between the columns is your missing number.
If the problem with that is that you don't know which side they go on, then you need to do some reviewing of the debit/credit rules. You have five kinds of accounts: assets, liabilities, equity, revenue and expense. Every account must go into one of the categories. Assets are debits, liabilities are credits, equity is credit, revenues are credits, and expenses are debits. That's just the normal balances, but there's more to it than that, and there's also unfortunately contra accounts to confuse the matter. If you need more help on that... Well, that could get a little difficult to do in this format, but I can do a brief overview of the rules... Or you can ask a specific question about something that confuses you.