The current Investment shows the amount invested in the stocks that you have right now. It doesn't include the amount you invested in the stocks you have already sold via Manage / Rebalance / Partial Exits.
It is the sum of investments into each of the stocks/ETFs & calculated as the total sum of the average buy price of each stock/ETF multiplied by the number of shares for that stock/ETF.
It is pretty simple. This is today's(current) value of your investments. If you sell your investments, you will receive the amount as in Current Value.
Money Put In
The Money Put In (MPI) amount will give you the total amount you have invested into the smallcase from your end. The MPI will not change if you sell some stocks,
In case of a rebalance or manage order which involves both sell and buy trades, the difference between the total buy amount & sell amount will be added to the MPI if the buy amt > sell amt. If not, the difference will not be adjusted in the MPI as there is no extra amount being invested into the smallcase from your end.
Say you bought 10 shares of a stock ABC at a price of Rs. 100 per share about a month ago
Your current investment is 10x100 = Rs. 1000
If the current price of the stock is Rs. 110 per share, the current value can be calculated as 10x110 = Rs. 1100
In total, you have invested Rs. 1000 into the stock & hence, your Money Put In until now is Rs. 1000
If during a rebalance, you have to sell ABC & buy 5 shares of XYZ at a price of Rs. 250 per share.
Sell amount for ABC = Rs. 1100
Buy amount for XYZ = 5x250 = Rs.1250
Since Buy amt > Sell amt, the difference of 1250-1100 = 150 will be added to your MPI which will be now MPI = 1000+150 = Rs. 1150
New Current Investment = 5x250 = 1250
Note: If the sell amt > buy amt, the MPI would have remained at Rs. 1000