Many fountain pens are cartridge/converter fountain pens, which means you can use either disposable cartridges (pop a cartridge in the back and throw out when empty, or refill cartridges with syringe) or you can a converter.
If you’re prone to accidents, you may want to use a paper or cloth underneath just in case. We like to live life on the edge.
Your converter may be a twist converter, but it follows the same concept as this, which you push up and down like a syringe.
Ensure your piston is all the way down.
Submerge your nib into the bottle of ink – make sure the whole nib is in the liquid. Pull up on or twist the converter to draw up ink.
You may find you have a sizeable air pocket because there was already air in the feed through which you drew up ink. You can push the ink and air back down, and draw up again a few times to get rid of the air.
Use a cloth or paper towel to dry off nib and grip section.
Put it all back together.
And you are good to go!