Your employer will send you Form 3922, Transfer of Stock Acquired Through an Employee Stock Purchase Plan Under Section 423(c), if you purchased ESPP stock during the tax year.
If you didn't sell any ESPP stock, don't enter anything from your 3922. Simply keep it with your tax or investment paperwork, in case you need to correct the cost basis when you later sell the shares.
Once you sell the shares, the brokerage firm that handles your ESPP should send you Form 1099-B, which reports the sale. If the cost basis in box 1e is wrong, here's where you can use your 3922: