Phew! This is a pretty basic query. When you invst in a mutual fund, there are 2 main ways of doing it:
1. Lumpsum investment - You basically put a sizeable amount in an MF scheme at once and wait for returns. It's a standard way of investing.
2. Systematic Investment Plan (SIP) - You invest a fixed sum of money in an MF Scheme once in a month / periodically over a period of time (1 year, 3, years, 5 years are common). SIPs are more convenient for the salaried class because they don't have large savings but they can afford to save a bit every month and invest so that they can build a corpus in the long-run. SIPs are also useful to small businessmen who can afford to save a specific amount of money every month without having to reinvest it in their business.
Which is more profitable? Ideally, it depends on timing. For instance, if you invest in a lumpsum at the right time, then you stand to gain a lot if the market goes up from there. However, if you invest lumpsum at the wrong time, you can make losses too. So basically, lumpsum investing makes most sense in trending markets. Whereas SIPs make most sense in sideways or falling markets. Why? Because your average price will be lower. If you invest through SIPs in a trending (rising) market, you're losing out because every month you will have to pay a higher price for the same stocks in the portfolio. You know what I mean?