Using a Bike Chain Tool

Step 4 Joining Chains

To link two chains together you need to have the Pin still through one of the outer plates of one chain's link. For the other chain you need the empty receiving roller side (narrow pair of plates) of a link. It looks just like prior picture.

First retract the Tool's Driving Pin so there is room to position the chain in the tool's lower support with the chain Pin protruding toward the Driving Pin.

Fit the two chain links together and line them up on the Chain Tool's lower support with the Chain Pin protruding toward the Driving Pin.

Then gently drive the Chain Pin in while gently steering the chain to keep things straight.
Be careful not to misalign so badly as to make the Chain Pin fold over in the plate hole.