Non cluster indexing with combination or on single entity for multiple columns

I am new to db design I also read concepts of non cluster indexing and know about the combined non cluster indexing but in my scenario I am having user table with multiple search on column

table column as follows   userName  fatherName  empId  cardNumber and so on. (above all 4 no one column is PK) 

I am having around 50 millions records over here due to large data search take huge time due to that I am thinking to create indexes in table but these all 4 searches are optional means possible user can fill all four or may be one or two of them but I was confused if I make all four separate index and one for all 4 then it might be creating issue on performance of while entering/inserting the data I created even a single index for all 4 column in combined but while I am searching with only card number then it takes huge time shall I created all four separate indexes would this work in combined search of empId and cardNumber

If I created separated once then what about combined searches If I create combinations then indices are 15 which obviously not a good way for insertion… lot of confusion I have can anyone help me thanks in advance