Coleus is the easiest plant to root, just cut about an inch off from the stem (no more than 2 to 3 leaves on it) and place it into a small pot with soil, water it lightly and place it in either artificial light or an east facing window. After about a week or so it should have roots already.
I start new plants quite frequently because it’s a good idea to constantly pinch back coleus for they grow a bit leggy. Pinching off tips also makes them branch out more and grow thicker stems. Never let the coleus flower in the fall season before bringing it indoors, they can decline. This plant from the photo above I took a cutting off and it was only an inch tall with just 2 leaves on it around 2 weeks ago. The key on growing coleus indoors is not to water them to often, keep them drier unless the season is late spring and summer.