support and resistance are points where price comes back and return again to the same point multiple times. These are the areas where majority of the trades hapen with good volume. the resistance genearlly will broken with heavy volume because the persons who bought at that level and stuck for long time will come out selling with a sigh of relief that their rate has come. so stock goes up breaking the resistance lines. The person who missed the rise after breaking or old one who sold think they made a mistake by selling early, again enter at the same price where they sold. so resistance beocmes support. The same logic applies to support once broken will become resistance. it is like a war situatoin. when two enemies are fighting, once they go in to enemy lines they occupy their bunker they making that as their support point, which is previouls a hurdle or resistance point