What are supports and resistances?

Supports and resistances are points in the price of an entity (it can be a share or a currency pair or a commodity or any other entity) where the prices stall. They have got more to do with history and user sentiment. Lets say that the price of the entity is 5 to begin with. It begins to rise and it keeps rising and seeing this price, more and more people would want to jump in and they keep buying and the price rises even more. This means that the demand is more than the supply and as long as this happens, the price will rise.
The price will continue to rise until a stage is reached where people start to feel that the price has become high enough or those who bought it early feel that they have earned enough profit. Lets say that at this point, the price of the entity is 10. So, people start feeling that the price has risen too much (this is also called overbought conditions) and slowly start selling. The demand becomes less than or equal to the supply and the price slowly drops from 10. As the price continues to drop, the people who plan to make money on shorts also jump in and the buyers (even though they might have very less profits or are in loss) start getting panicky and they start selling and the price starts falling more and also at a faster rate.
So the price continues to drop from 10 and thus 10 becomes resistance as the price has not breached 10. Next time the price comes close to 10, the buyers and the sellers will look at past history and find that 10 was the place where selling started the previous time and so the buyers would want to get out at that point just to be on the safer side and so 10 becomes a even bigger resistance.
The price drop from 10 continues and at one place, the opposite to the one explained above happens ie. the users feel that the price has dropped too much (say at 2) and they start buying again and the price starts to rise again. Thus 2 becomes the support.
Remember, the greater the amount of time that a support or resistance has not been broken, the stronger it is. Even yesterdays high and low are resistance and support respectively but they are not very strong as they are quite recent prices.
So, always watch out for supports and resistances. The big banks and traders dont sit with their ema or whatever indicators and buy and sell based on that. They look out for stops and resistances and buy / sell based on that. So be careful, watch out for opportunities and get a feel of the market before jumping in.