This is what bootloader/fastboot mode normally looks like, so it seems the phone is doing exactly what you told it to do. It’s now waiting for commands; you’ll need to attach the phone to your computer via USB and issue commands using
I’m guessing you’re trying to install TWRP recovery as lineage usually is installed from TWRP. There’s instructions on which fastboot commands to issue here. Note that you only need to perform one of the listed install methods - so if you’ve used the app install method, you don’t need the fastboot install method (and vice-versa).
P.S. General reminder: remember to back up any/all data that you want to keep before starting these kind of procedures.
P.P.S. More discussion about installing lineage can be found in the topic over here.