"I have never been to buy marijuana before and I am unclear as to why I need a recommendation and what this means from a medical standpoint. "
Since a doctor cannot give you a prescription for marijuana he can give you a recommendation, but not all doctors ill do this, because at this time it is still illegal. And the laws differ from state to state.
Technically, a doctor cannot write you a 'prescription' because cannabis is a Schedule 1 drug, and it is therefore federally illegal for a doctor to do this. As a result, state laws have been enacted saying that a doctor can make you a 'recommendation' which allows you to purchase cannabis products under state law.
Be aware, that you are technically still breaking federal law, since state law does not change the illegality of the federal classification. However, the Feds have issued guidance saying they are unlikely to enforce federal laws against people that are compliant with their local state laws in this regard.
Dispensaries and delivery services all want to make sure they are compliant with state laws, and so they will make sure you have a valid doctors recommendation before selling you anything.
Any doctor with an valid license in CA can write you this 'recommendation' however you will find that many are uncomfortable with the process, or feel inadequately informed of the potential medical effects of cannabis, and so they are likely to just refer you a doctor with more experience with cannabis.
If you are not in California, your local state laws may be significantly different to this. You may for example have to register as a patient with the state (in addition to getting the doctors recommendation.) Additionally, some states may only allow for a restricted set of medical conditions they will certify patients for, or they may have no medical marijuana laws at all, in which case the federal illegality still applies and may be enforced.
I hope this helps clarify the issue. Its a complicated legal landscape, and one that is changing rapidly across the country and the world.