Demand curves will differ as some markets will have a flat demand curve where there is perfect competition. This is when there are too many competitors selling homogenous goods. Generally the demand curve slopes downwards as price increases of a product but it all depends on the type of goods also being sold so this is what causes the differences.
An upward-sloping supply curve means that there is a relationship between the price at which a product is given and the quantity demanded by customers. Sellers in that market will likely react by also pricing their goods around same price as the market or slightly lower to gain a few customers who would be interested in lower prices, but they also would not want to do this too much as they can lose out on profits that the market is making.
