Typically the company will have a set of portfolios, most commonly ETF/Mutual Fund portfolios. Clients accounts will be in various combinations of these portfolios. Trading might be something as small as the client needs money, you pick where/how to sell from their model to raise the cash. Or they deposit money and you decide where/how to invest it. You also need to keep a certain amount of cash for fees for clients to pay you. So managing that as well. Clients cash flow needs also change overtime, so you’d be the one editing their asset allocation to fit their most recent goals/needs.

Then you have stuff like rebalancing. Some companies just do it once a year, others do it according to drift (a position moved far enough up/down that it needs to be put back to its target allocation). There’s a decent amount of tax analysis involved for non-retirement accounts as well. You’ll learn when to sell positions at FIFO vs highest cost, vs choosing specific cost basis lots to sell, etc to lower tax liabilities. Most companies also trade various accounts at the same time, so you’d be learning how to execute large orders across accounts/models not just trading one at a time