My pattern says to K3 and place these sts on hold, k to last three, place last 3 sts
Hmm..i'm guessing it means to put those 3 on a stitch holder? But thats my guess....
What are you making? Can you link to the pattern? The line as written isn't very clear.
Leave them on the needle if they will be used again soon (in a few rows). If it will be awhile (many rows) then put them on a safety pin (great for so few stitches).