Becoming a vendor that accepts bitcoins means that you'll have to establish a bitcoin account.  Payments made to you will be deposited into this account.  You also need a Point-of-Sale (POS) system to accept the payment transaction.

There are fees associated with accepting bitcoins.  They may come in the form of a monthly fee or a transaction fee. 
 
Start by checking with your current POS service provider.  Ask them if they provide bitcoin processing on their system. 
 
If your current POS service provider does not provide the service utilize any of these POS services to process bitcoin payments:
 
ALFA Coins
Bitcoinpay
Bitpay
Coiknbase
Coinify
CoinPayments
DC POS
FogPay
Gocoin
Mollie
PaxFul
Revel Systems
Shopify
SpectroCoin
Stripe
XBTerminal