Can Satan harm me?

Not unless God allows him to do so.

For example, Jesus told Peter that Satan had requested that God allow him to "sift" Peter. It was not allowed in that case. Satan, on the other hand, was allowed to bring great troubles to Job, but couldn't take his life.

The Bible says that Satan is a "destroyer":

"Neither murmur ye, as some of them also murmured, and were destroyed of the destroyer" (1 Corinthians 10:10).

"A dreadful sound [is] in his ears: in prosperity the destroyer shall come upon him" (Job 15:21).

"Concerning the works of men, by the word of thy lips I have kept [me from] the paths of the destroyer" (Psalm 17:4).

Peter, under divine inspiration, said:

"Be sober, be vigilant; because your adversary the devil, as a roaring lion, walketh about, seeking whom he may devour" (1 Peter 5:8).

To be sober-minded is to be in Christ, faithfully doing what God desires in our lives. Being vigilant is guarding against the wiles of the devil. This is done through Holy Spirit discernment that comes with seeking God's will in all things.