Stock Grants from Employer- How are they treated?

So it does not vest at all, and then vests fully in one lump sum in 2020?

By default, no tax impact occurs on the grant until 2020, at which time the FMV of the stock (as of the vesting date in 2020) is considered income to you.

There is an election called a "Section 83b" election (named after the tax code section that governs this) that allows you to be taxed on the FMV as of the date of grant (i.e. in 2016) instead of the vesting date (i.e. 2020).

If this is something you want to consider, you need to speak directly with a CPA as this is a rather complex situation.

Why would you do this? Let's say the stock is valued at $2 today, but you think the business is about to take off, and in 4 years, it will be valued at $10. It might make sense to pay the tax on $2 today vs the tax on $10 in four years.

Have a follow up question about this.
I've usually just let it be, but I've done some research and I'm leaning towards filing an 83 b.

I know you have to file within thirty days but...question is, when is the money "due"? As in, do you send in a check when you file or do you use the form the following year when you file your taxes?

Guessing it's the latter since it's based on income

Most grants vest in percentages each year. Example 75 shares over 3 years. Each year 1/3 (25 shares) become vested and you can choose to sell for current market value or do nothing if you think the stock will increase in value. If you decide to cash out the 25 shares typically you can they will deduct shares to cover taxes. They cut you a check for balance.