Ticks are very small, only 1 to 3 millimetres. They are easy to miss. If you have just been bitten by a tick, at first it will look like a small black dot on your skin. Once they bite, ticks start drinking blood. After several days, they swell up to a brown or grey ball the size of a pea.
The first image below, from the RIVM video about removing ticks when you find them, shows a recently attached tick in the fold of an elbow.
The second image below shows a tick that has already bitten into the skin.
The illustration below shows how a tick attaches itself to the skin.