uri gajogeun jumalmada gongwoneseo sanchaekhaeyo.

주말마다 literally breaks down to 주말 (weekend) + -마다 (every). So it means “every weekend.”

• 매주 means “every week,” regardless of day.
• 주말에 means “on the weekend” (once, or unspecified how often).

Use 주말마다 when you want to say you do something each and every weekend.

The particle 에서 marks the place where an action occurs (“at,” “in,” or “from” when it’s a source of action).

• 공원에서 산책해요 = “(We) take a walk at the park.”
  On the other hand, 에 can mark a location of existence (“to be at” or “to go to”), or a time point:
• 공원에 있어요 = “(We) are at the park.”
• 공원에 가요 = “(We) go to the park.”

산책해요 is the polite present tense of the verb 산책하다 (散策-하다), which means “to take a walk” or “to stroll.”

• 산책 is a Sino-Korean noun meaning “walk” or “stroll.”
• 하다 is the verb “to do.”
  When you conjugate -하다 verbs in polite speech, 하다 → 해요, so 산책하다 → 산책해요.

The standard Korean word order here is:

1. Topic: 우리 가족은
2. Time adverbial: 주말마다
3. Location adverbial: 공원에서
4. Verb: 산책해요

So you get “As for our family (우리 가족은), every weekend (주말마다), at the park (공원에서), we take a walk (산책해요).”
Korean is relatively flexible, but changing the order will shift emphasis. For example, putting 공원에서 first can foreground the place:

• 공원에서 우리 가족은 주말마다 산책해요.
  It still makes sense, but sounds like you’re emphasizing 공원에서 (“At the park…”).