Your wireless network and the speed promised to you by your ISP are separate entities and are affected by different phenomena.
If your ISP only supplies 10 Mbps that is all you will get, regardless of your wireless router or access point. In the US for example, fiber optic (FiOS) is very generally capable of 50 Mbps, cable Internet may be about 20, and DSL could be 2. These are very approximate. No wireless access point will improve upon them.
If your wireless network environment is "noisy" due to any number of variables, your best option is to utilize the Express's 5 GHz network, to the extent your equipment can use it. Only iPads and the newest iPhone or iPod Touch models are capable of using 5 GHz. Macs have been able to use 5 GHz for several years.
5 GHz is less susceptible to interference from competing wireless networks, but is more susceptible to attenuation due to the presence of intervening objects or building materials. 5 GHz may result in better speed, but this may be at the cost of reduced range. Aboslute answers are elusive due to many unknown factors in wireless networking.
Thanks for trying to help me but I'm far from technical I have sky TV and have connected the airport express to the sky router. Airport express is now showing as a network connection independently but I was expecting it to enhance my Sky connection and enhance the speed. At least that's what the salesman said would happen! Have I just been suckered?
Thanks again John
Have I just been suckered?
Well, the AirPort Express cannot "boost", or "extend", or "repeat" the wireless signal from a Sky router by using wireless only, so you may want to have conversation with the salesman.
The AirPort Express can only "extend" a wireless network if you have another Apple router providing the network.
From Apple's literature sheet on the Express:
Extend an existing Wi-Fi network’s range.
If you already have a wireless network in your home and want to extend its range, AirPort Express can help. Just place it in range of your primary base station — an AirPort Extreme, Time Capsule, or another AirPort Express