Many people often confuse these three elements of graphic design as the same thing. Although they interconnect with each other they have distinctive differences.
Your logo is the face of your brand and corporate identity. It is the visual equivalent of your companies reception desk and is quite often also found upon your reception desk. It is 90% sure to be the first impression your company gives. So I don't need to tell you how important it is to get this right.
A logo could be placed on just about any surface. It could be engraved into metal, plastered on a motorway banner advertisement, put on the top of your letterhead or printed onto the back of a bus ticket. Therefore it needs to look as good in monochrome as it does in full colour. The key element to logo design almost definitely is its shape. It must be clear, visible, easily interpreted and must not rely on colour to separate different elements.
Your corporate identity is the manner in which your business presents itself to the public. In it's simplest form your corporate identities are your policies and processes. The core fundamentals of your business and how you want it to be perceived. Corporate identity is often confused with brand identity but the two are distinctly different. Compared with a car, your corporate identity is your components like your engine, battery and fuel tank. Your brand identity is like your seatbelts, seats and soft furnishings and your logo is the shape and colour on the outside. In order for the car to look and function its best, these three components must synchronise and work together. This is similar to your logo, brand, and corporate identity.
Your brand identity is the consistent look of your company throughout everywhere that it appears. This includes your logo, business cards, posters, banners, flyers but also includes your office decor, furnishings, fonts, vehicles, letters, official documents etc. Imagine anywhere you can put your logo is part of your brand identity and it should be consistent, easily recognisable and complimentary.
To cut a long story short these templated graphics are not capable of being trademarked. When you are building your brand you need to ensure that you are building it for the long term. Whereas these sites are great for your everyday handypeople and solo tradesmen they are not sufficient when you are trying to build a company or enterprise. If you invest in your brand now you will save a lot more money in the long term having to re-advertise and market to customers you have already won.