You should be able to add a new WCF service project from the solution root in Solution Explorer...
Right-Click >> Add >> New Project
It's not clear from your question what 'doesn't work' though.
Your newly added project will need to reference the existing project that contains the methods that you want to access. You should perhaps consider if your current design is appropriate - ensure that you have separated out your presentation code (this should be your website project) from the common business functions that you want to share (I would have this as a separate class library project in the solution). Your WCF project can then reference the common 'business logic' project.
To reference your 'business logic' project from the WCF project...
Right-Click (on WCF project) >> Add Reference