Thank you for posting & welcome to the community !!
You can replace the wick when it gets damaged over a period of time due to hard water build-up or root tissue growing through the wicks. In this case, just remove the wick by pulling it out with the help of a small tweezer and insert the new one.
Caps are for controlling over-saturation in the soil, particularly for succulents. If you plan to grow succulents, make sure you use one of those caps. Simply place and fix it over the wick tube.
Speaking about the longer wick, it should be halved before using. Cut it in the center and make two wicks out of it and use them when needed. Hope you’ll find it helpful. If you face any problem please do let us know, we’ll be more than happy to help you! Happy growing!!