In short, genealogy is the study of family history. Aside from studying birth records, historical lists and articles and other available sources, relatively recently popular method of studying family history is DNA analysis, to see how related people within a DNA database are. There are two biggest consumer focused companies out there for humans: Ancestry, which is mostly focused on North America and MyHeritage, which is mostly focused on Europe.
My uncle started doing genealogy on MyHeritage and I was kinda fed up myself with not knowing all the cousins, their spouses, children. I also wanted to have my DNA sequenced. After all, I used to work in such a company, but eventually I opted to first enter the data in Ancestry because their DNA database of humans is the biggest there is at the moment, they offer traits display, as well as ancestry, and there's an option to export the data from them and import it into MyHeritage. It took some manual work to export the data from Ancestry, with usual disclaimers, of course, then import it to MyHeritage and wait for them to analyze it.
DNA is assembled by combining some parts in the DNA strain of the individual with the reference genome. Humans are mostly the same so there are no big differences between us regarding genetics.
All of the calculations are done by finding similarities of the submitted DNA with the rest of the DNA samples in the database.
The ancestry analysis is done by comparing the number of DNA subsequences of the individual with the sampled population grouped by their place of living. It is a static picture of things. People migrated and there's considerable room for getting it wrong, but there is truth to it, especially because ancestry can be distinguished way back throughout generations.
The traits display is there to see things like free vs attached earlobes, alcohol flush, sprinter gene and so on. Ancestry got almost all of my traits correct. Traits are usually determined by finding genetic similarities of a user within the DNA database that is marked up by user submitted answers.
More interesting is the PRS (Polygenic Risk Score) that can determine predisposition to various traits. Diseases being a very interesting part of it. Cancers and such. Of course, we're talking about statistical probability, which is definitely not the singular cause, but a possible contributing factor. For instance, just because one might be an alcoholic, genetically speaking, if they're not drinking, it can hardly be the case. PRS are also most viable in the populations with European ancestry, since they're the most researched group, but can fail in other groups. Take it with a grain of salt if you're checking things out for health. Ancestry does not give out PRS related to health. If one wants that, they should sequence their genome with 23andMe instead.
DNA analysis, as expected, depends largely on the sample size, as well as other factors, like epigenetics, additive genetic effects, etc. It is an interesting area of study.
It took about a month to get the results. The kit gets ordered, sent, then it's activated, sample is collected via saliva, stabilizing fluid is added to it and it's mailed back. It's a long wait then. They need to receive the sample, extract the DNA and run analysis on it. It depends on the lab and the amount of work they have. Import/export to another service (from Ancestry to MyHeritage in our case) was a matter of days and a bit of manual work.
As for my ancestry, I didn't get swapped at birth. The DNA matches it produced are correct, from both sides of the family (calculated by chromosomes because this is how inheritance works), but the ancestry is different from what I was expecting. My family is Slavic, to be precise: West and South Slavs. In Ancestry.com instead of Czechia, it got a lot of Southern Poland. It also threw out some similarities in their model with Germanic Europe, Baltic, Sweden and Denmark, then a bit of Norway. MyHeritage used a different model because it has different groups and has different samples. They placed my ancestry correctly in Czechia, but also found some similarities with Greek and Italian groups, Scandinavian, Iberian and Finnish. Apparently the families migrated from the north towards the south of Europe. Can't really blame them. My path was going back and a bit west. I'm in Ireland now and I love the climate here. I even got the citizenship just a few days ago ☘ Something to mess up the static image of ancestry once again :)