Hello and welcome to Simviation
You can find a lot of good advice here and have gotten some good ideas already
Like one post stated FSX is a CPU and RAM hog.
These are the things that effect FSX and how well your system can perform then
There is no particular order here
AI traffic keep it down
Cloud draw distance keep it at a reasonable amount
one of the biggest killers is the autogen textures and what is called bloom keep them down
Tuning FSX to any one system is best described as trial and error. Find out what does not work and than back down from that.
Scenery detail and Aircraft detail is another killer
Weather is another big factor
If you want to see the worst case scenario set up a thunder storm and than use a highly detailed aircraft at a highly detailed airport and you will quickly find out where you stand.
With your specs stay away from highly detailed scenery as you will only be disappointed
Frame rates should be set to a max of 20 in your case do not use unlocked frame rates as this will cause your CPU to try to achieve the higher settings and it will not be able to.
Of course there is the FSX CFG file this is where you can really tweak your settings.
If you read the sticky post at the top of this forum they will help you a lot
Just take your time as there is no short cut
There are lessons you can take built into FSX that will help as well, But I suggest that you find a aircraft that is to your liking but for now stay away from any plane with jet engines until you can handle the propeller aircraft.
There is a ground school that will teach you how and why planes work.
In the real world real pilots start out in ground school before ever getting into any aircraft.
And do not be afraid to ask any questions here no matter how stupid or dumb you may think they are.
This is a lot of information here but like I said take it slowly and you will be flying in no time.
People like myself Fozzer and others who have been flying for a long time are only to glad to help out in any way we can
