After getting on disability,they paid lump sum of money from when they thought disability should have started.do I pay taxes on that money at the end of the year

If the disability income is from a disability policy or program paid for by your employer, then, yes, you WILL pay taxes on this lump-sum income.

If it is Social Security Disability or VA disability or it is from a disability insurance policy that YOU paid for from a private insurance company, it is NOT taxable.