questions about connecting to sql server express

Hi

I have installed sql server 2019 with SSMS locally on my computer. The name of the sql server is xyz_1120_11. 

When i start SSMS, i see as server name not only  xyz_1120_11 but also  xyz_1120_11\\SQLEXPRESS  and  xyz_1120_11\\SQLEXPRESS01.

1) Why is this?

Then, I use windows authentification, and when i try to connect with xyz_1120_11, i get the error "the server was not found or not accessible". Same error when i try with xyz_1120_11\\SQLEXPRESS. But  with xyz_1120_11\\SQLEXPRESS01, it works.

2) What's the reason of this?

Thanks