How do I earn social security credits, and how many do I need to qualify for SSDI?

The following answer is from: https://faq.ssa.gov/link/portal/34011/34019/Article/3829/How-do-I-earn-Social-Security-credits-and-how-many-do-I-need-to-qualify-for-benefits

We use your total yearly earnings to figure your Social Security credits. The amount needed for a credit in 2019 is $1,360.  You can earn a maximum of four credits for any year. The amount needed to earn one credit increases automatically each year when average wages increase.

You must earn a certain number of credits to qualify for Social Security benefits. The number of credits you need depends on your age when you apply and the type of benefit application. No one needs more than 40 credits for any Social Security benefit.

The following answer is Attorney Walter Hnot’s annotated response to the previous answer. 

What does that even mean right?!  I remember the first time I read that years and years ago, I sat back and thought, what the heck are they talking about.  First off, quarters of coverage are the same thing as credits.  Think of credits as a coin.  Every time you work, like shoveling, filing paperwork, creating an invoice, whatever…you earn money, and when you pay taxes on it to the federal government, you can earn credits, or quarters of coverage.  Ok so you are shoveling dirt, boss man pays you $1,300.  You pay taxes on that $1,300 to the federal government, so you will end up with something around $850 - $1,100, depending on what tax bracket you are in.  The government will then acknowledge that you are a good soldier of society, and they will give you one coin, or credit, or quarter of coverage.  You can get up to 4 of these a year…wahoo right.  So, if you earn $1,300, and then keep working and earn it 3 more times, you will get a total of 4 coins for the year.  These coins should just be called insurance coins, and you should imagine them sitting on your belt as small little metal medallions.  As you get older, you need more of them for that year’s age (like 54 years old) in your life.  If you don’t have enough, then at that point in time, for that year that you didn’t have enough, you become, “uninsured.”  If you are uninsured, even if you are severely disabled during that uninsured year, too bad, so sad, you can’t start claiming SSDI for that year.  Ok so here is the trick, since you can’t use that uninsured year, we need to prove that you were severely disabled in prior years where you were insured, or putting it another way, had enough coins on your belt for that age.