The letter at the end of the tax code refers to your situation and how it affects your tax-free Personal Allowance.
L: applies to most people born after 5 April 1938 with one job.
K: applies to somebody with taxable benefits greater than this year’s Personal Allowance. Although K codes are designed to collect extra tax, the amount of tax collected each pay period cannot be more than half of the earnings for that period.
BR: means that no Personal Allowance is available against this source of income. This generally applies to a second job, where one job is allocated all of the Personal Allowance and the other is taxed at basic rate.
DO: similar to the BR code, except that earnings from this source of income will be taxed at higher rate tax. This applies when HMRC expect other sources of income to exceed the basic rate threshold.