ReadyBoost is a Windows feature that uses USB sticks or other flash drives such as SD cards to "speed up your computer". However the concrete use is not to add the device's memory to your RAM but to use fast accessible devices as cache storage.
Because of this fact, there are certain conditions that have to be met. The first of course is that you use a flash drive with high reading-rates and access times. If these are lower than those of your hard drive, it will give you nothing. The second is, that you do not turn off your computer every time you complete your work - if you do so every evening, the cache on your flash drive will not even get the chance to properly build up to be used before you shut the computer down. The better choice is to hibernate your computer.
Hibernation is disabled by default on many computers and is not available in the shutdown menu. You can circumvent this however by entering the following into an elevated command prompt (search for cmd, right-click it and Run as administrator):
powercfg -H on
Afterwards right-click on your desktop and create a new shortcut pointing to shutdown.exe /h. Using this shortcut will cause your machine to go into hibernated state (your computer does not use any power here - it just saves the state the current programs are in and cleans the RAM cache, they are restored to that state after turning on the machine again. This happens using a large file where the states are stored in).
Upon hibernating, the flash cache will not be deleted and hence unfolds its use over time.
Another important issue is writing on drives and the defragmentation of drives. The more you write on the drive, the more the flash cache has to be changed - this can result in lower efficiency. If you also defragment the drive, you damage your cache even more - at some point it will become ineffective. Do that only before you choose to completely restart or shutdown your computer (turn off auto defragmentation if you have such things enabled by some kind of software!). Of course, trying to defragment the flash cache will make it unusable.
If you have everything prepared, insert your flash device into the machine. On the what-to-do-with-it prompt, choose Speed up my system using Windows ReadyBoost. Remember not to defragment, restart or shutdown the machine to be able to fully use the device.
Now if you have a decent amount of cache on your flash drive and requests are send to open something, the RAM cache is the first location to look at - if there is nothing there but on your ReadyBoosted drive, the computer will calculate whether it is faster to get the files from your cache or from your hard drive - this is the way ReadyBoost actually can make your machine faster and it has nothing to do with increasing RAM or similar issues.