$\frac{1}{8}$ can be represented by a grid divided into eight equal parts with one part shaded.

$\frac{2}{8}$ can be represented by a grid divided into eight equal parts with two parts shaded.

$\frac{3}{8}$ can be represented by a grid divided into eight equal parts with three parts shaded.

So, the model below represents the number sentence.

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The first fraction circle is divided into three equal parts with one part shaded.
So, the first fraction circle represents $\frac{1}{3}$.

The second fraction circle is divided into three equal parts with one part shaded.
So, the second fraction circle represents $\frac{1}{3}$.

Combine the shaded pieces into one fraction circle.

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The sum of the two fractions is represented by a fraction circle divided into three equal parts with two parts shaded.
So, the sum is $\frac{2}{3}$.

Therefore, the number sentence $\frac{1}{3}+\frac{1}{3}=\frac{2}{3}$ can be used to find the sum of the fractions.

$\frac{3}{5}$ can be represented by a fraction strip divided into five equal parts with three parts shaded.

$\frac{1}{5}$ can be represented by a fraction strip divided into five equal parts with one part shaded.

$\frac{2}{5}$ can be represented by a fraction strip divided into five equal parts with two parts shaded.

So, the model below represents the number sentence.

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The first fraction circle is divided into seven equal parts with six parts shaded.
So, the first fraction circle represents $\frac{6}{7}$.

The second fraction circle is divided into seven equal parts with five parts shaded.
So, the second fraction circle represents $\frac{5}{7}$.

There are five shaded pieces in the second fraction circle.
Remove five shaded pieces from the first fraction circle to find the difference.

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The difference of the two fractions is represented by a fraction circle divided into seven equal parts with one part shaded.
So, the difference is $\frac{1}{7}$.

Therefore, the number sentence $\frac{6}{7}-\frac{5}{7}=\frac{1}{7}$ can be used to find the difference of the fractions.