Зимой мы катаемся на лыжах в парке.

Russian often uses the instrumental form of the seasons as adverbs of time.

• зима → зимой = in winter
• весна → весной = in spring
• лето → летом = in summer
• осень → осенью = in autumn

So зимой is a very normal, idiomatic way to say in winter or during winter.

Here катаемся comes from кататься and means something like we go riding, we ride, or in this context specifically we ski.

By itself, кататься is a broad verb used for recreational movement:

• кататься на лыжах = to ski
• кататься на коньках = to skate
• кататься на санках = to sled

So катаемся does not by itself mean specifically ski. It is на лыжах that makes the meaning specific.

The -ся ending is the reflexive marker, but here it is not best translated literally as ourselves.

A useful contrast is:

• катать = to roll something, to give someone a ride
• кататься = to ride around oneself, to go riding, to engage in the activity

So мы катаемся means we are riding / we go riding, not we ride ourselves in a literal English sense.

Many Russian verbs with -ся are just learned as separate vocabulary items, and this is one of them.

Russian normally says кататься на лыжах for to ski.

Literally, it is something like to ride on skis. The preposition на is commonly used with things you ride on or use for this kind of activity:

• на лыжах = on skis
• на коньках = on skates
• на санках = on a sled / sleds
• на велосипеде = on a bicycle

So на лыжах is just the standard Russian expression here.

Because лыжи means skis, and skiing is normally done on a pair of skis.

So Russian says:

• лыжи = skis
• на лыжах = on skis

The singular лыжа does exist and means a ski, but when talking about the activity, Russian naturally uses the plural.

Лыжах is in the prepositional plural.

The basic noun is лыжи. After на in this expression, it becomes на лыжах.

For a learner, the most important thing is to remember the whole phrase:

• кататься на лыжах

It is best learned as one unit, because this combination is extremely common.

В парке means in the park.

When Russian expresses location with в meaning in, it usually uses the prepositional case:

• парк = park
• в парке = in the park

So в парке tells you where the skiing happens.

Not necessarily.

Even though катаемся is a present-tense form, with зимой the sentence normally describes a habitual action:

• Зимой мы катаемся на лыжах в парке.
• In winter we ski in the park.

So this is more like a regular activity or general fact, not necessarily something happening at this exact moment.

Because the sentence describes a repeated or habitual activity.

Кататься is imperfective, and imperfective verbs are used for:

• ongoing actions
• repeated actions
• general habits

Since зимой suggests something that happens regularly during that season, the imperfective is the natural choice.

A perfective form such as покататься would mean something more like to go skiing for a while / to have a skiing outing, not a general seasonal habit.

Yes, very often.

Russian verb endings usually show the subject clearly. The ending -емся already tells you this is we.

So both are possible:

• Зимой мы катаемся на лыжах в парке.
• Зимой катаемся на лыжах в парке.

Including мы can make the sentence clearer, more explicit, or slightly more emphatic, especially in beginner materials.

Yes. Russian word order is flexible.

This version is neutral and natural:

• Зимой мы катаемся на лыжах в парке.

But you could also say:

• Мы зимой катаемся на лыжах в парке.
• В парке зимой мы катаемся на лыжах.

The basic meaning stays the same, but the focus shifts a little. Putting зимой first sets the time frame right away, which is a very common Russian pattern.