Just starting out, using a MacBook Pro (Early 2015 10.14.3) I have a RCA jack from my old record player plugged into headphone jack on my Mac with 3.5 jack. Only option On Recording Device is Built -in Microphone, can I get another option or do I need get a USB convertor for my record player?
13"? The 13 inch had a setup service where it tried to get the one connection to do everything.
Apple (upper left) > System Preferences > Sound. Somewhere in those settings should be the ability to make the single connection be stereo for recording. Then you need a cable much like this one.
To connect the record player you may need small female to female adapters if your record player is cable-only.
If what you really have is a turntable, then you will need an adapter such as the Behringer UFO-202 which has both a simple stereo connection and is switchable to the three connections needed for an RIAA cartridge compensation from a turntable. The third cable is the thin black wire with the spade connection on the end.
Note the extra thumb screw on the left (for the black wire) and the switch from Line to PHONO.