The picker that lets a customer choose a pickup point before checkout lives in your theme, so it needs one switch turning on. You enable it once and it works on every page that has a cart. It has no settings of its own in the theme editor: everything it does is configured inside the app.
On Dashboard, find the row Locker selection in cart under Operational status. While the picker is off, the button there reads Enable in theme. It opens the theme editor directly at the app embed, so you do not have to hunt for it.
In the theme editor, open App embeds in the left panel, switch the embed on and save. One thing surprises people: the embed is named Wybór Paczkomatu on every store, including English ones. That is the name Shopify shows, and it is the right embed.
Back on Dashboard, the Locker selection in cart badge flips to Active. Now open your storefront, add something to the cart and look next to the checkout button. On an English storefront the panel reads InPost locker with a Choose point button. On a product page it appears only inside the cart drawer. For customers outside the markets the app serves, currently Poland and Italy, the cart looks exactly as it did before.
Add the post-purchase blocks as well, see Add pickup selection to the Thank you and Order status pages.
Set the rate the app should treat as pickup delivery in Settings → Delivery method.
If the panel does not show up in your cart, work through The pickup picker does not appear in my cart.
Stuck on any of this? Open the chat in the bottom right corner of the app and we will help you set it up.