Are you the personal representative?
You might want to start by reading IRS Publication 559 (link below).
Generally, however, a cash inheritance (or property acquired via operation of law at the death of a co-tenant) is not a taxable event except in certain instances (e.g., a retirement account).
Interest earned on the account will be reported to you by the bank and should be reported on your tax return.
The account was a joint account with you and your mother. You should check with the executor of your mother's estate to ensure there are no inheritance tax implications on the funds transferring to you upon her death.