kono kami ha usui node, nimai kasanete tukaimasu.

は marks 紙 as the topic of the sentence: as for this paper...

So この紙は薄いので means something like:

• As for this paper, since it is thin...

It does not mean the paper is doing an action. It just sets this paper up as the thing being talked about.

A learner might expect が, but は is very natural here because the speaker is making a statement about this paper as a general topic.

Because 薄い is an い-adjective, and before ので you use the adjective in its plain form:

• 薄い + ので → 薄いので

So:

• 紙は薄いので = because the paper is thin

You do not use 薄くので here.

For comparison:

• 薄くて is possible, but that uses て, not ので
• 薄いので specifically gives a reason or cause

ので means because / since, and it gives the reason for the main action.

Here:

• この紙は薄いので、二枚重ねて使います
• Since this paper is thin, I use two sheets stacked together

Compared with から, ので often sounds a bit softer, more explanatory, and slightly more formal or neutral.

Very roughly:

• 薄いから = because it’s thin
• 薄いので = since it’s thin / because it’s thin

Both are possible, but ので fits well in explanatory statements like this.

枚 is the counter for thin, flat objects such as:

• paper
• shirts
• plates
• tickets

So for sheets of paper, 二枚 is the natural choice.

• 一枚 = one sheet
• 二枚 = two sheets
• 三枚 = three sheets

Using 二つ would sound unnatural here, because つ is a general counter and not the normal one for paper.

It refers to two sheets of paper.

Even though 紙 is mentioned earlier, Japanese often avoids repeating nouns when they are already clear from context. So 二枚 by itself is enough to mean:

• two sheets
• understood as two sheets of this paper

A more expanded version would be something like:

• この紙は薄いので、二枚の紙を重ねて使います

But the original sentence is more natural because it avoids unnecessary repetition.

重ねて is the て-form of 重ねる, which means to pile up, stack, layer, or place one on top of another.

In this sentence, it means the sheets are used layered together or stacked one on top of the other.

So:

• 二枚重ねて使います = use two sheets stacked together

This does not just mean use two sheets separately. It specifically means the two sheets are overlapped/layered.

The て-form connects actions.

Here the sequence is:

1. 重ねて = stack/layer them
2. 使います = use them

So the sentence means:

• I stack two sheets together and use them
• more naturally, I use two sheets layered together

The て-form often works like and, but here it also suggests the first action is done as part of the way the second action is carried out.

It is omitted because it is obvious from context.

Japanese often leaves out words that can be understood. Here, the omitted object is the paper / the sheets of paper.

So the full idea is something like:

• I stack two sheets of this paper together and use them

But Japanese normally does not need to say all of that explicitly if the listener already knows what is being discussed.

In Japanese, the non-past form can express:

• habitual actions
• general facts
• future actions

Here it describes a habitual or usual practice:

• Because this paper is thin, I use two sheets together

So 使います does not necessarily mean I will use only once. It can mean I use in general.

It means I use two sheets layered together.

That is, the speaker is not treating the two sheets as separate items for separate use. The point is that the paper is thin, so they compensate by making it effectively thicker through layering.

So the nuance is closer to:

• I use it doubled
• I use two sheets at once
• I layer two sheets together when using it

You could say that in simple English, but pieces is not the best match here.

Because 紙 is paper and 枚 is the counter for flat sheets, the idea is more specifically:

• two sheets
• two sheets of paper

Also, 重ねて adds an important detail: they are stacked together. So a fuller translation would be:

• Since this paper is thin, I use two sheets stacked together

That captures the Japanese more accurately than just I use two pieces.