How would you make money ?

[whyBish]

Instead of buying stocks as a long term investment (1,2,3 ..years),wouldn't it be better to buy and resell the stocks on the same day/week ? I know someone who makes money by buying stocks in the morning and then reselling on the same day

The term for this is "day traders". It is much riskier than investing in the long term, and I wouldn't recommend it without knowing what you are doing... (even if you do know what you are doing I still wouldn't recommend it, but that's only my personal preference.)

Just some more (basic) detail for those that are interested:
Basically the scheme is that 'technical traders' plot some graphs and find patterns in stock movements and trade on those, rather than the underlying fundamentals of the stock. (You will hear terms like support levels and such.). The idea is that larger traders (such as fund managers) perform their actions on a regular basis, and so the market as a whole for that stock will have exploitable patterns (well there are a whole bunch of other things that can lead to patterns too, such as day of the week, seasonal variation and so on.). The risk is, past performance doesn't guarantee future performance, things can go against the trends, and you can lose big. The standard ways that day traders deal with this are to use the methods of diversification (day-trading over multiple stocks), and hedging (buying a 'put' on the stock being traded, which is similar to insurance, and can limit your downside losses). Since day-traders trade on potentially small patterns they require larger sums of money to make a profit after brokerage (brokerage and amount of funds available are the limiting factors to entry into day-trading), so it is usually left to the 'big boys'.