achimmada keopireul masineun geosi seupgwanieyo.

마다 is a particle meaning “every,” attaching directly to a noun.

• 아침마다 = “every morning.”
  You can also say 매일 아침, literally “daily morning.” In most contexts they’re interchangeable, but:
• 아침마다 emphasizes each individual morning as a repeated event.
• 매일 아침 highlights the overall frequency (every day).

Korean uses 것 to nominalize (turn into a noun) an action.

• 마시다 (“to drink”) becomes 마시는 것 (“the act of drinking”) by:
  
  1. 마시
     • -는 (present attributive suffix) → 마시는
  2. Attach 것 → 마시는 것
     This noun phrase can then serve as the subject of 습관이다.

Korean has two subject markers: 이 (after a consonant) and 가 (after a vowel).

• 것 ends in the consonant ㅅ, so it takes 이 → 것이.
  This marks 마시는 것 as the subject for the copula 이다.

1) 아침마다 커피를 마시는 게 습관이에요

• 게 is a colloquial contraction of 것이.
• Meaning is identical, just a bit more casual.
  2) 아침마다 커피를 마시는 습관이 있어요
• Uses 습관이 있다 (“to have a habit of…”) instead of 습관이다.
• Translates as “I have a habit of drinking coffee every morning.”
  Both are natural:
  
  • ~습관이에요 states the action itself is a habit.
  • ~습관이 있어요 says you possess that habit.