Here are the steps to take to fill a Sketch marker with Various ink.
First you want to remove the nib with your fingers, or with tweezers.
Remove the cap off your various ink bottle & attach the booster needle. Carefully remove the protective cap & insert the needle into your marker.
You will feel some resistance, but go ahead & continue to push the needle into the sponge. Squeeze the ink bottle until the appropriate amount of ink is in the marker. The following are empty marker maximum fill amounts;
Copic 5 cc
Wide 6 cc
Try not to overfill your marker, but if you do, you can use rubbing alcohol to wipe everything clean. Replace the marker nib in the direction shown printed on the marker. Color will begin to appear on the nib in a few minutes. Replace the marker cap. Thoroughly clean the booster needle with Copic colorless blender or rubbing alcohol. Replace your protective cap & replace the cap on your various ink.
Nibs come in various styles;
Starting on the left side & going down you'll see nib #1 which is the Standard Broad style. #2 is a Soft Broad, #3 Caligraphy 5 mm, #4 is a Round nib & #5 is what's called a Brush.
Then begining on the right & going down you see #1)Stand fine, #2 Super fine, #3 a Semi Broad, & #4 the Caligraphy 3mm.