My neck is darker than my face and I really want to know what to do to make it light and blend with my facial tone

Please have a good read of this FAQ.
It will help you decide what is best for you to use.
https://www.askmehelpdesk.com/skin-lightening/skin-lightening-frequently-asked-questions-190905.html
Also, remember to use a good sunblock to help prevent darkening.