Если тебе хочется, мы можем перекусить в кафе у метро, а потом пойти в парк.

Если means if and introduces a conditional clause. In Russian, when an если-clause comes first, it’s normally followed by a comma before the main clause:

• Если тебе хочется, мы можем… = If you feel like it, we can… If you reverse the order, the comma is still usually used:
• Мы можем…, если тебе хочется.

тебе хочется is an impersonal construction meaning you feel like (doing something) / you’re in the mood. Literally it’s like to you it is wished (dative + “desire happens”).

• тебе = to you (dative case of ты)
• хочется = one feels like / wants (in a spontaneous, mood-based way) ты хочешь is more direct and intentional: you want (something).
  Compare:
• Ты хочешь перекусить? = Do you want to eat? (a straightforward request)
• Тебе хочется перекусить? = Do you feel like having a bite? (more about mood)

Because хотеться (the verb behind хочется) takes the experiencer in the dative: the person who “feels like” something is marked as to/for someone. So:

• мне хочется = I feel like
• тебе хочется = you feel like
• ему/ей хочется = he/she feels like
• нам хочется = we feel like
• им хочется = they feel like

It can be complete as-is. Если тебе хочется works like If you want / If you’d like and leaves the “what” implied by the following suggestion.
You can also make it explicit:

• Если тебе хочется перекусить, мы можем… = If you feel like having a snack, we can…

In this context мы можем means we can in the sense of it’s possible / we could (a suggestion/option). It’s not about permission so much as offering a plan:

• Мы можем перекусить… = We can grab a bite… A very close English equivalent is We could…

перекусить means to have a snack / grab a bite to eat (a quick, light eat).
It’s perfective, so it focuses on completing the action once:

• перекусить (perfective) = have a snack (once, get it done) The imperfective would be перекусывать (habitual/repeated) or перекусывать/перекусать depending on context:
• Я обычно перекусываю в 5. = I usually snack at 5.

Russian uses в + accusative for motion into/to and в + prepositional for location in. Here в кафе looks identical because кафе is indeclinable (it doesn’t change form), but the underlying logic is:

• Motion: пойти/заехать в кафе (accusative; form happens to match)
• Location: сидеть в кафе (prepositional; form also matches) So в кафе can mean to a café in this context because it’s paired with an action like перекусить (go there and eat).

у + genitive means by/near/at (next to) something:

• у метро = near the metro (station) It’s not “inside the metro”; it’s in the vicinity of it.
  Genitive here: метро is indeclinable, so it stays метро, but grammatically it’s genitive after у.

That’s exactly what it means. Russian often stacks location phrases like this:

• в кафе (the place)
• у метро (where that place is located) So: in a café near the metro station.

а потом means and then / and after that, but а often adds a sense of sequencing or contrast between steps (“first this, then that”):

• …перекусить…, а потом пойти… = …grab a bite, and then go… и потом is also possible, but а потом is very common for “next step” narration.

пойти is perfective and usually means to set off / to go (once, start going). After потом it naturally expresses the next completed step in a plan:

• потом пойти в парк = then (we’ll) go to the park / head to the park идти would sound like focusing on the process of walking/going rather than the planned transition:
• потом идти в парк can be used, but it often feels less like a neat “step” and more like “then be going/walking to the park.”

Russian often omits repeated subjects when they’re obvious from context. мы is already established in мы можем, so it’s understood for пойти too.
You can say:

• …а потом пойти в парк (more like “and then (to) go…”, a plan/option) Or more explicitly and future-like:
• …а потом мы пойдём в парк = and then we’ll go to the park

It’s informal and friendly because it uses тебе (singular you) and a soft suggestion structure:

• Если тебе хочется, мы можем… = If you’d like, we could… It’s polite in a casual way—more gentle than a direct Пойдём… (Let’s go…).