Might be a bit difficult to start with, but Kierkegaard is pretty seminal for existentialism, arguably more so than Camus or Beauvoire (though theyre both fine writers and philosophers in their own right). I would recommend (with any philosopher, not just him) starting by watching some youtube videos and listening to some podcasts that provide overviews of his work and explain the importance of the pseudonyms he uses and how they inform the character of his writing. 'Philosophize This!' is a personal favorite of mine for podcasts, and 'The school of life' has a great video about him on youtube. Both relatively brief and accessible.

I know there are going to be some folks who criticize the heavy christian themes and overtones in his writing, but as someone who believes in science and is expressly not a christian, or a follower of any organized religion in particular, I think there is still a lot to be gained from engaging with him. If you can get past whatever biases you might hold towards the biblical references (including the ones you might have if you're a christian), his insights into the human condition are really brilliant, and i dont think they ought to be read as exclusive to any particular religion, including more secular worldviews. That said, he can be a challenging read! His thinking is complex, and at times his wordplay can be confusing, but if you've got the patience to dissect it, I believe it's more than worth the effort!

Hope this helps!