The following is a short primer in Y-DNA testing and what kind of results you can expect to receive from your test: 

There are two different, but related Y-DNA tests that are useful in genetic genealogy. STR testing is the recommended test for first-time testers. A 37 marker test will provide you with your unique haplotype, and will also give you a predicted haplogroup. Once you have tested, you will be able to join the surname project, and depending on your haplotype, you will be placed with your closest matches in a subgroup. If you have many close matches, you may want to consider upgrading to 111 markers in order to further refine your relatedness with your matches.

The other Y-DNA testing method that is available is called SNP testing, either testing individual SNPs or via the Big Y-700 test. SNP testing confirms your haplogroup, which is a group of similar haplotypes that share a common ancestor. That common ancestor may have lived many thousands of years ago, and therefore is not really useful for genealogical research. However, with advanced SNP testing like the Big Y-700 test, you can discover your terminal haplogroup (or your most recent common ancestor), which depending on who else has upgraded, may have lived within the genealogical era (i.e. the last 500 years).

Our ancestors that first carried these unique mutations, or SNPs, lived many thousands of years ago, long before the advent of the written record or surnames. Since we don’t know their names, when they are discovered they are given alphanumeric names like U106 or M222. Each ancestor, or SNP, once discovered, is then added to a huge patrilineal family tree, called the phylogenetic tree. Each SNP represents an ancestor (or group of ancestors since each SNP is roughly calculated to occur over several generations) that lived and died sometime in the past, and their descendants carried their unique SNP mutations down to the present day.

For example, here is a SNP descendancy chart that visually explains the phylogenetic tree. http://www.ytree.net/DisplayTree.php?blockID=160. Their shared common ancestor is designated as SNP L1065, who is believed to have been alive circa 44 AD. All of the SNPs below him are his descendants, shown down to the present day. What this information does is to allow genetic genealogists the ability to very finely differentiate between similar haplotypes, sorting them into explicitly defined groups of related testers (haplogroups).

The SNP descendancy is displayed in short-hand on the results page in each subgroup heading. For example, one subgroup contains the following SNP hierarchy: 1 R1b > P312 > Z290 > L21/S145 > DF13 > ZZ10 > MC14 > Y16773 > PF3873 > A7298 > A7300. R1b is estimated to have lived circa 18,500 years ago, or circa 16,550 BC.  P312 is estimated to have lived circa 2676 BC. SNP Z290 is estimated to have lived circa 2632 BC. SNP L21 is estimated to have lived circa 2587 BC. SNP DF13 is estimated to have lived circa 2145 BC. SNP ZZ10 is estimated to have lived circa 2108 BC. SNP MC14 is estimated to have lived circa 2026 BC. SNP Y16773 is estimated to have lived circa 500 BC. SNP PF3873 is estimated to have lived circa 476 BC. SNP A7298 is estimated to have been alive circa 423 BC. And their terminal SNP 7300 is estimated to have been alive circa 220 BC. 

All of the members in this subgroup are either proven through SNP testing or determined by STR matching to descend from the same common ancestor. Further SNP testing via the Big Y700 test will provide more answers, and more shared SNPs (ancestors) will soon be discovered. Genetic genealogy is still a very new science, and you can be part of the discovery process by participating in Y-DNA SNP testing. Your terminal SNP is your last known shared ancestor with another tester, and will change as more men are tested and more variant SNPs are discovered and named.