Firstly, let's assume that your employer only gives you the statutory minimum holidays anyway. (If that's not the case, and your employer is more generous, we've got no figures to work on because we don't know the details of your contract).
I'll also assume that you work 5 days per week, so your holiday entitlement for the full year is 5.6 x 5 days = 28 days. (If you work 6 days per week your entitlement is still 28 days for the full year because it's capped at that level. If you only work 4, or fewer, days per week, you'll need to multiply that number of days by 5.6 to work out your annual entitlement).
You've not said when your employment actually ends, so I'll assume (for illustrative purposes) that it's towards the end of this month, on Friday 28 March. We'd then be 31+28+28 days (= 87 days) into the year, so your holiday entitlement would then be 87/365 of 28 days. To do that sum you need to multiply 28 by 87 and then divide by 365. That gives you 6.67 days. (Obviously, you'll need to modify that sum according to when you actually finish work).
Then, although you say that you've not taken any holidays yet, you need to remember that any 'enforced' holidays (e.g. when the business was closed) still count as part of your entitlement. So if I assume that your employer's business was closed on Wed 1st January, you'd then only have 5.57 days of holiday owing to you.
Once you've worked out the relevant figure, you need to remember that your employer is free to decide when you take your holidays (or don't take them, as the case may be), as long as you're given reasonable notice. So your employer could, for example, insist that you take 5 days holiday as the final 5 days of your employment period (and just add pay for 0.57 of a day onto your final pay) or he could insist that you work without holidays until the very last day (and then add 5.57 days of pay onto your final pay).