To use an arpeggiated pattern with a chord on the guitar means to play each string separately rather than strumming them all at once. Arpeggiated chords are laid out in a specific fashion when reading notation or tablature: Rather than placing the notes or numbers directly on top of one another, which indicates a single strum, they will be slightly to the left or right of one another. This indicates that the notes should be played separately.
Start with a basic chord shape. For example, try out Em. With Em, all the strings are strummed. When using an arpeggiated pattern for this chord, each string is played separately.
Use a pick or your thumb to pick each string in succession, from the heaviest to the lightest.
Play each string from the top with the exception of the lightest string; pick this string from below.
Play each string going in the opposite direction, from lightest string to the heaviest. Practice going up and down the strings a few times in the arpeggio manner.
Switch to a new chord and continue plucking the strings in the same manner. If you're playing a chord such as A, Am or C, only pluck the strings that you're supposed to play with regular strumming.