K2‘SSN ，please help!

[ping1015 0]

Today my child and I went to the social security office to get SSN(social security number).

The lady said we must apply the employment authorization card first and then can apply

k2' SSN.She said we can fill out the I-688B or I-766 forms to get the employment authorization card,and must

go to apply in person.

So now I am confused,I saw on USCIS web site,the I-765 is the form that applies EAD(employment authorization document) ,

What is the different between the forms,I-765,I-766and I-688B?

Which is the form that K2 visa apply EAD?

Do we need to go the office in person?

Thanks..