sli 20

hello I want to SLI my MSI Ventus 2080 ti GP edition. I own an ASUS ROG x570-E motherboard. MSI Ventus 2080 ti GP supports 2-way SLI. what is a 2 way SLI and how to do it? secondly, I searched for MSI SLI bridge, it says my GPU should be in 1st and 4th slot, what does that mean?