What is this powershell syntax doing? -

i've come across following powershell syntax:

([adsi]"") 

i realise active directory, want understand syntax doing.

can explain me?

i different results these two:

[adsi] | get-member [adsi]"" | get-member 

what quotes doing?

adsi on it's own not recognized, square brackets doing?

is same new-object adsi("")

i different results these two:

[adsi] | get-member [adsi]"" | get-member 

the first 1 enumerating member of type adsi. second 1 enumerating members of object (and instance) of type adsi.