Step 1: Reusable Version
2.thread ink through cap so that the tip is on the inside of the cap
3.put cap back on
4. Reverse the process to use pen
Step 2: Retractable Version
Step 3: Remove the Ink
Step 4: Get a Pencil Sharpener With a Big Opening
Sharpen the end part until the little black thing comes out, you should have a hollow tube like this (mine has tape on it because I couldn't find a sharpener like the one i used to have so I used pliers to crack the pen and take the piece out, also it marks the back)
Step 5: Assembly
Ink goes in backwards, then endcap, then cap
Step 6: Ta Dah!
Flick to extend and press down to put back, have fun and be smart, remember there are other pens you could use for this, so don't be afraid to make some things up!