VC firms are a group of General Partners that have raised an investment fund from Limited Partners -- educational institutions, foundations, wealthy individuals, and major businesses. LPs are a VC firm's backers; they're not making investment decisions in the companies themselves. The GPs are running the firm. They're active investors that are watching different markets and choosing companies to invest in that match their investment strategy.
As a startup founder, anytime you're thinking of a partner at a VC firm, you're thinking of a General Partner. They're the ones you're trying to reach; preferably through a direct introduction, but sometimes through meeting a VC firm's associates, who at many firms are the ones actively going to events and otherwise 'sourcing deals' (finding companies).
Venture Hacks has a good article about how VC firms and Limited Partners interact: http://venturehacks.com/articles/history-of-investors (among many other great articles for founders looking to raise money).