Could you please explain taqdeer and how us as Muslims should understand and accept taqdeer.

Answer

Yes, all good and bad are from Allah Ta'ala. No one can fathom the wisdom and mysteries of Allah Ta'ala. Shaitaan is bad/evil. Who created him? There is no other creator besides Allah Ta'ala. If Allah Ta'ala had not willed the creation of evil, He would not have created Iblees.

Furthermore, Allah Ta'ala allows Shaitaan to execute whatever evil he desires. So too is our evil nafs. This evil propensity in us has been created by Allah Ta'ala. There is no evil in the Malaaikah because Allah Ta'ala did not create an evil nafs for them. If Allah Ta'ala had willed us to be as sinless as the Angels, He would not have created an evil nafs in us.

Taqdeer cannot be explained. Even on the Day of Qiyaamah, the Ambiyaa too will not fully understand Taqdeer. Rasulullah (Sallallahu alayhi wasallam) forbade the Sahaabah from probing into this issue. It is a forbidden domain. The more you try to understand it, the more confused you will become. Then in your state of confusion shaitaan will intervene to shake and even ruin your Imaan.

Since our Nabi (Sallallahu alayhi wasallam) has angrily warned the Sahaabah against this topic, we do not venture to explain something which cannever be adequately explained.