Looseness in gear lever

[Vinay-RS]

Hi all, 

Recently I was told that my gear selector is a little loose and that something might need replacing (forgot what exactly). I was wondering where I should start to investigate and whether it would be a job I could tackle myself? Please note, I am still pretty useless at most technical jobs    
I was also curious what the replacement parts might cost, as cash is a wee bit tight at the moment. 

Thanks,

Vinay