Investment management is key for every person in Finance and the Stock market. With IM, everyone can act smartly and according to their decision. You can decide to act by Technical Analysis and you decide to act by philology of your mind and even only by reading news.
To become investment management, you should, firstly, understand your client /yourself, who are they/you? like what do you want your portfolio works, passive income (replicate the performance of the market), or active income (try to beat the market)?
Secondly, you need to build a strategy. A strategy built from tactical asset allocation by the indexes you like to determine your investment like PER vs MSCI World.
Thirdly, you need to understand that investment management is all about managing RISK! you should be aware of the risk on the market like Country risk(a situation happening in the country and its effect on the market countries), Market risk (if the market undervalues or overvalued), Currency risk (the value of an investment made in a foreign country changes due to variations in exchange rates), Liquidity risk (when the time comes to sell an asset, no one is there to buy it from you at a decent price, as the situation on 2020 crash by fear of Coronavirus), Inflation risk(increasing of high rates to fight with shortest in the market like happening nowadays), Shortfall risk(your portfolio didn't perform as you wanted). To manage all the risks is DIVERSIFICATION!
Fourthly, you need a suitable strategy on basis of Marco's picture, Market volatility, and Market valuation.
I hope I help you understand what is Investment management and what marks you need to know and how to act according to them.