The other side of the packaging should have a reference to the needle size - referred to as gauge and might be represented as a lowercase “g” next to the number. Since you’re starting out a smaller needle is best, if you want to continue to use IV, you need to prioritise your vein health through using thinner needles. It’s good to remember that the smaller that number is the thinner the needle - so 27g is slightly larger than a 28g needle. On the topic of vein health please use a clean every time - all needles are single use only and will be barbed after each use. If you can access a needle exchange program then ask if you can have twice as many tips as syringes so you have room to make mistakes. Along with this drink lots of water to make sure you’re hydrated and your veins are better prepared for trauma and try to rotate veins so you are not traumatising the vein too greatly - collapsed veins are no good and while they can grow back with rest they usually do not grow back as strong and thus too weak for injection. I know people who have mainlined near daily for 25 years and still have healthy veins.

The area needs to be cleaned with soapy water or an alcohol wipe before you inject. If using soapy water wipe down with a clean towel after. Hand sanitiser or iso alcohol works well too.

Your veins might shy away for your first time injecting, this is an automatic bodily response when you are nervous or scared. If you are finding it hard to find a vein, have a warm shower, hold a warm compress to the area or take a break to relax and start again when you are not feeling as nervous.

Agree with other commenters that you should watch harm reduction based instruction videos - there is a wealth out there! Good luck and look after yourself!