amido no tikaku ni monohosi ga aru node, sentakumono wo hosu toki ni benri desu.

It has two main parts:

• 網戸の近くに物干しがあるので
  = because there is a clothes-drying rack / clothesline near the screen

• 洗濯物を干すときに便利です
  = it is convenient when hanging laundry

So the pattern is:

• reason clause + ので
• main statement

A very literal flow is:

• Near the screen, there is a clothes-drying thing, so
• when hanging laundry, it is convenient

Japanese often puts the reason first and the conclusion second.

Because 近く is functioning like a noun meaning vicinity or area nearby.

So:

• 網戸の近く = the area near the screen
• 駅の近く = the area near the station
• 家の近く = the area near the house

This is the very common pattern:

• A の 近く = near A

Because ある is an existence verb, and the place where something exists is marked with に.

So:

• 網戸の近くに物干しがある
  = there is a drying rack near the screen

Compare:

• 机の上に本がある = there is a book on the desk
• 庭に木がある = there is a tree in the yard

If this were an action happening near the screen, you might see で instead, but with ある, に is the normal choice.

Because ある usually marks the thing that exists with が.

• 物干しがある = there is a drying rack

Here, 物干し is the thing being introduced as existing in that place, so が is natural.

If you used は, it would sound more like you are already talking about the drying rack as a topic:

• 物干しは網戸の近くにある
  = as for the drying rack, it is near the screen

Both can be correct, but they have different focus.

Because 物干し is an inanimate thing.

• ある = used for things
• いる = used for people and animals

So:

• 物干しがある = there is a drying rack
• 猫がいる = there is a cat

Both ので and から can mean because, but ので usually sounds a little softer, more explanatory, and more matter-of-fact.

• あるので = because there is, so...
• あるから = because there is, so...

In a descriptive sentence like this, ので sounds very natural. It feels a bit like giving a practical reason.

A rough nuance difference:

• ので = explanatory, softer, slightly more objective
• から = more direct, more speaker-driven

Because 干す is a transitive verb, meaning to hang/dry something.

So the laundry is the object, not the doer:

• 洗濯物を干す = to hang the laundry
• 洗濯物が干す would incorrectly make the laundry the one doing the action

That is why を is used.

とき means when or at the time of.

So:

• 洗濯物を干すとき = when hanging laundry
• 洗濯物を干すときに便利です = it is convenient when hanging laundry

Here, the phrase tells you the situation in which something is convenient.

Not always strictly necessary, but it is very natural here.

You will hear both:

• 洗濯物を干すとき便利です
• 洗濯物を干すときに便利です

The version with に clearly marks the time/situation in which the convenience applies, so it sounds smooth and standard.

Also, with words like 便利, 不便, 必要, and similar expressions, Japanese often likes clearly marked relationships, so ときに便利です sounds very natural.

Because 便利 is a な-adjective.

For な-adjectives:

• before a noun: use な
• at the end of a sentence: do not use な

So:

• 便利な場所 = a convenient place
• この場所は便利です = this place is convenient

That is why the sentence ends with 便利です, not 便利なです.

Japanese leaves that unstated.

In English, we naturally say it is convenient, but Japanese often omits that kind of subject when it is obvious from context.

Here, what is convenient is basically:

• having the drying rack there
• that location/setup
• the situation as a whole

So the idea is:

• Because there is a drying rack near the screen, it is convenient when hanging laundry.

Not everything that is understood in English needs to be said explicitly in Japanese.

物干し is a general word for something used to hang laundry to dry.

Depending on context, it could mean:

• a clothesline
• a drying rack
• a drying pole
• a laundry-hanging fixture

So the exact English word depends on the real-life object being described.

網戸 refers to a mesh screen used on a door or window to keep insects out while letting air in.

Depending on the situation, it may be translated as:

• screen door
• window screen
• insect screen

So if the sentence’s translation says screen door, that is a contextual choice, not the only possible translation.

Yes, and that is a very common alternative.

• 洗濯物を干すときに便利です
  = it is convenient when hanging laundry

• 洗濯物を干すのに便利です
  = it is convenient for hanging laundry

The difference is small:

• ときに focuses on the time or situation
• のに focuses more on the purpose or use

Both are natural, but のに便利 is especially common when talking about what something is useful for.