Can anyone explain how associations work in ABAP CDS?

Hi

I am new to CDS modeling and trying to understand how an association exactly work

Please find the below mentioned code and explain me how exactly an association work
depending on where path expressions are used

Regards

Srujan

select from bkpf  association [0..1] to t001t  as _b 
on $projection.mandt = _b.mandt
and $projection.bukrs = _b.bukrs
{
    key bkpf.bukrs ,
    bkpf.mandt,
    bkpf.belnr ,
    bkpf.gjahr ,
    _b.ltext
}
where _b.txtna = 'F_0001_FOOTER'