To add a new instruction in parallel with an existing instruction, move the cursor above or below the existing instruction (by clicking, or by using the up and down arrow keys), and then insert the new instruction.

For example, starting from an empty rung you could type:

L <Down> L <Left> C <Down> <Down> <Left> C

The result is two series sub-circuits (each of contacts and a coil) in parallel.

Similarly, to insert a new instruction in series, place the cursor to the left or to the right of the existing instruction (by clicking, or by using the right or left arrow keys). Then insert the new instruction.

Note that you can't insert the instructions in arbitrary order. For example, if you started by inserting one coil and one contacts in series, then you could add a new coil in parallel with the existing coil, but you couldn't add the new contacts-coil sub-circuit in parallel with the existing circuit. So it's important to plan what you're drawing before you start inserting instructions.