naneun jumalmada mateueseo jangboneun de han siganjjeum sseo.

나는 uses the topic marker -는/은, which sets “as for me…” and often sounds natural for general habits or routines.
내가 uses the subject marker -가/이 and is more common when you’re emphasizing who does it (e.g., 내가 해 = “I do it (not someone else)”).

주말마다 = “every weekend”.
The particle -마다 attaches to a noun meaning “each/every” instance of it:

• 날마다 = every day
• 달마다 = every month
• 사람마다 = each person (everyone)

마트 is a very common shortened loanword from (super)market. In everyday speech Koreans often say 마트 rather than the longer 슈퍼마켓. It commonly refers to grocery stores, supermarkets, or big-box marts.

-에서 marks the location where an action happens (“at/in” + action location). Since 장보다 is an action (shopping), you use:

• 마트에서 장보다 = shop at the mart

-에 is more about destination or existence:

• 마트에 가다 = go to the mart
• 마트에 있다 = be at the mart

장보다 specifically means to buy groceries / do grocery shopping (shopping for food and household necessities).
쇼핑하다 is broader: shopping in general (clothes, browsing, etc.).
So 장보다 strongly suggests practical grocery shopping.

V-(으)ㄴ/는 데 turns a verb into a noun-like phrase meaning “(the act/process of) doing V”, often used with time/cost/effort:

• 장보는 데 한 시간 = “one hour for grocery shopping” / “it takes one hour to grocery shop”
• 공부하는 데 돈을 많이 써 = “I spend a lot of money on studying”

Here, 장보다 → 장보는 데 (“in/for the act of grocery shopping”).

Not here. 데 can mean place, but in V-(으)ㄴ/는 데 it’s part of a grammar pattern meaning “doing V / the process of V”.
So 장보는 데 is not “the place where you shop,” but “(spending time) on shopping.”

쯤 means “about/approximately”.
So 한 시간쯤 is “about an hour”, implying it’s an estimate, not an exact timed hour.

You can say 한 시간을 써, but in casual Korean the object marker -을/를 is often omitted when it’s obvious.
So 한 시간쯤 써 is a natural spoken shortcut for 한 시간쯤 (시간을) 써.

써 is the casual (intimate) speech level of 쓰다 (“to use/spend”).
Other levels:

• 써요 = polite casual
• 씁니다 = formal

This sentence sounds like casual conversation with a friend.

With time/money/effort, 쓰다 commonly means “to spend”:

• 시간을 쓰다 = spend time
• 돈을 쓰다 = spend money

Because the thing being “used” is 한 시간쯤 (time), it’s understood as spend.

It’s a habitual present meaning “I (usually) spend”, supported by 주말마다 (“every weekend”). Korean present forms often cover general habits/routines, not just “right now.”

Yes, 장보는 데 is the standard spacing for the grammar pattern V-(으)ㄴ/는 데.
You may also see 장보는 데에 in some contexts, but in this “time spent” structure, 데 alone is very common and natural:

• 장보는 데 한 시간쯤 써 (natural)