If you recommend a person or thing is to vouch for them. Recommend can also be to advise. If your doctor recommended an exercise program to you that's changed your life, you might recommend your doctor to your friends.
Recommend is connected to the verb commend "to praise." They are both spelled with one c and two m's, reflecting the prefixes re- and com-. These verbs overlap in some uses: you can recommend or commend an applicant for employment. But commend is used for special or public praise: "He was commended for bravery."