How do I input my income made money through app’s/online selling platforms such as Poshmark, Vinted, Mercari, Etc? H

It's a fairly straightforward process.  Please see the TurboTax Help article How do I report income from self-employment? for guidance on entering these payments.

You're generally considered to be self-employed if you work as an independent contractor, consultant or freelancer, even if you also have a salaried job.