This is the 55th most frequent Japanese word.
でき
"でき" means "can," "ability," or "completion" depending on context.
The word 'できます' (dekimasu) here is used to express the ability to perform an action, in this case, 'to eat and drink' inside the store.
店内での飲食ができます。
You can eat and drink inside the store.
The word 'できました' (dekimashita) here is used to indicate the successful establishment or creation of something, in this context, 'a new friend' as a relationship.
新しい友達ができました。
I made a new friend.
The word 'できました' (dekimashita) here conveys the successful completion or result of creating something, in this case, the cake being cooked well.