Transact SQL :: Write Parameter Stored Procedure In Server?

I am having table on which i want to fire a query on.

table structure is as follows :

Table1 

Table1ID    bigint PK
City  nvarchar(10)
FirstName  nvarchar(10)
LastName  nvarchar(10)
MiddleName  nvarchar(10)
State  nvarchar(10)
FirstName  nvarchar(10)
LastName  nvarchar(10)
LLDCode     nvarchar(20)
MMDCode    nvarchar(20)
LastModified    datetime
CreatedDateTime       datetime
LastUpdatedDateTime       datetime
SSN#  nvarchar(20)

I have to write a parameterised stored procedure where multiple values will be pass as input to SP.

E:g:  1) SSN# if no record found by SSN# then 2) Find by LLDCode OR MMDCode

This logic can be implemented using UNION to join output of 2 queries and selecting by LastUpdatedDateTime this query will return the Table1ID.

Now we will fire the query on table2 where this Table1ID as FK in Table2 and we will return the filed SSXML from Table2.How to do this ?

Table2 structure.

Table2ID PK
Table1ID FK
Name
Department
SSXML