An IP address is the address of the server your emails are sent from. Providers such as Gmail and Outlook look at the history of both your domain and this IP when deciding between the inbox and spam.
Shared IP: all plans send from Outfound's shared sending IP by default. There is nothing to set up or choose. Reputation on the shared IP is protected by rules that constantly watch bounce and complaint rates.
Dedicated IP: a sending IP reserved for your organization only. Its reputation depends entirely on your own sending and is not affected by other senders. It can be added to any plan for 2,490 TRY per month (VAT included).
A dedicated IP is not required. It helps if you send regularly at high volume and want your reputation kept separate. A new dedicated IP builds reputation through gradual warm-up, so it does not send at full volume straight away.