Karma as the Ethical Center
In Buddhism, actions matter. And therefore karma serves as an ethical compass for your life. Karma is not a complicated concept. It is as simple as this: What you do, what you say, and what you feel will have an effect.
Effects of Actions
You can taste the effects of some types of karma right away, but other karmic actions will bear fruit at some point in the future. Karma points to the realization that everything is interconnected in some way.
But your actions have much greater effect than one day's span. Karma is a process of constant change. If you do skillful acts now you can change your later karma. For Buddhists, the belief in karma is a guiding moral compass. However, do not worry or obsess on past actions. Take care of your life today. Live in the moment and change the present. Thereby you can change the future as well.
Traditionally, Buddhists would undertake their lives in a way to maximize their skillful karma by generating merit. They do this by donating food to begging Buddhist monks, donating money to the monastery, and doing good deeds. If you live your life in accordance with the Buddhist teachings and moral principles, you will automatically be on the way towards generating merit and limiting unskillful or destructive karma.
Whatever the ultimate truth of karma and rebirth, it can't hurt to live a good life that seeks to limit harming others and seeks to be less selfish and more generous (in fact, research suggests generous people are happier). Another important consideration about karma is that not all suffering is the result of karma. Local conditions such as temperature and internal conditions such as a virus have nothing to do with your karma. It is only through deep wisdom (prajna) that you would be able to know which bits of suffering are due to past karma and which are due to local conditions. Uncertainty winds up being the order of the day.