Wat are the best palces to invest money from there I get fixed monthly income.
Not sure of your locality. In the USA, there are many options.
There are many corporate bonds that pay interest monthly.
You can invest in a handful of bonds, chosen so at least one of them pays interest each month. (Minimum investment requirements make this an expensive option)
Unit Trusts made of bonds (a handful of bonds wrapped into a single fixed investment) usually pay monthly interest. As the bonds begin to mature, the interest payments shrink (but you begin to get principal payments which can be reinvested).
Bond mutual funds and ETFs usually provide monthly dividends (that come from the interest and capital gains of the bonds held by the fund). Dividends are usually consistent, but not necessarily fixed.
You can produce a monthly income from stocks in the same way as the above mentioned bond methods. Income can be consistent, but not fixed.