Merging information

I have an excel file containing two sets of (hopefully identical) serial numbers, the second set has significantly fewer serial numbers but also contains more different relevant information, if it is possible to match up the two sets of serial numbers with the additional information that pertains to them that would be the ideal. If anyone can help I would be grateful. The Vlookups that I have already done are not working properly I'm sure I'm messing something up so if help is available for that as well as every little bit helps!
Thank you