I want to invest in SIP. Where and how much should I invest?

You can choose a good Direct Mutual Fund platform to start investing in SIPs. See this answer on how to select a good platform: Ram Kalyan Medury’s answer to What is the best site or app for investing in direct mutual funds through SIP?

How much to invest depends on your income and expense levels. It would be ideal to save atleast 30% of your after tax income. Those who save upto 50% become financially free in 15–20 years. This means that they do not have to depend on a job for their living anymore.