If your boots leak, waterproof socks can be a cheap fix. But they're thicker than normal socks, so you need to have enough give in your boots.
As for waterproof, there are basically three kinds you can choose from
* Expensive waterproof textiles. These are waterproof. GoreTex is the best, but others come close. They'll leak a bit in downpour but otherwise they're 100%.
* Medium price waterproof textiles. These will keep you dry in a shower, keep you damp in rain, and make sure you're soaked in a downpour.
* Cheap rain suits that go over your normal kit (leathers or textiles). They're are a pain, because you'll want to take them off when it's not raining, but you need to stop and put them back on when it starts again. But they do the job. They're the best option if you're on a budget. You can get separate jacket and pants, or a 1-piece. Separates are easier to get on when the wind's blowing a hoolie.