The graphics settings you choose in game determine the performance and visuals in game. Finding a good balance between FPS and "eye candy" is essential for getting the most out of the game.
Resolution - this determines the number of pixels that are shown horizontally and vertically. Generally speaking you should always be using the max setting possible for your monitor and if your FPS is so low that you are considering lowering this setting then your computer probably doesn't meet the system requirements of Shadow Company.
Texture filtering - Unlike most other games instead of changing the level of texture filtering you can change the type. Essentially each one is a different method of smoothing out the edges of objects and "transparent" objects such as railings. Bilinear filtering is the least intense and has the lowest performance impact and anisotriphic point is the most effective at smoothing edges while having the largest impact on performance. Presumably the level of intensity must be manually changed in your graphics card settings.
Vertical Sync - This setting smooths out your frame rate by locking your frame rate to the refresh rate of the screen. Sometimes your monitor will display part of two different frames at the same time (this is called "tearing") and Vertical Sync fixes this problem. On the other hand vertical sync also delays the frames to smooth them out which is really annoying for pro gamers. In general it is best to disable this setting unless you are getting really bad tearing.