Normally Mac OS X uses RAM efficiently.
What exact Mac do you have and how much RAM does it have?
Have a look at Activity Monitor (Applications / Utilities /) and check the "System Memory" tab to see what your "Page ins:", "Page outs:" and "Swap used:" are.
image below uses sorting by CPU as an example
He clearly didn't read your original post
Restart the computer, when you hear the Start Up Tone hold down the Option key. Then select the Recovery Partition - Disk Utility and run Repair Disk Permissions at least 2x, while in DU run Repair Disk 2x as well. Then restart the computer in Safe Mode. To restart in SM when you hear the Start Up Tone hold down the Shift key until you see a progress bar. A Safe Mode restart will clear some caches. After the SM restart restart normally and test.
The "Activity Monitor" screenshot showed that three quarters of the memory is "free". "Free" means it isn't used at all, your computer would run exactly the same if that memory wasn't there. In other words, freeing memory wouldn't make any difference whatsoever. In other words, you are looking for an answer to the wrong question.
To get the answer to your actual question, your description of your problems is so vague that it is completely useless. Describe _exactly_ what is actually your problem.