הסדין הלבן נקי, אבל השמיכה הכחולה עדיין בסל הכביסה.

ה־ is the Hebrew definite article, meaning the.

So:

• סדין = a sheet / sheet
• הסדין = the sheet

In this sentence, the speaker is talking about a specific sheet, so Hebrew uses הסדין.

In Hebrew, adjectives usually come after the noun, not before it.

So:

• הסדין הלבן = literally the sheet the-white
• natural English: the white sheet

This is the normal Hebrew word order:

• noun + adjective

Examples:

• הבית הגדול = the big house
• החולצה הירוקה = the green shirt

Because the noun הסדין is definite, the adjective must also be definite.

In Hebrew, adjectives agree with the noun in:

• definiteness
• gender
• number

So if you say:

• סדין לבן = a white sheet
• הסדין הלבן = the white sheet

Both the noun and the adjective take ה־ when the phrase is definite.

Hebrew usually does not use a present-tense word for is / am / are in simple sentences like this.

So:

• הסדין הלבן נקי
  literally: the white sheet clean
• natural English: the white sheet is clean

This is called a nominal sentence. In the present tense, Hebrew often just puts:

• subject + description

Examples:

• הילד עייף = the boy is tired
• הדלת פתוחה = the door is open

Because סדין is a masculine singular noun, and the adjective must match it.

So:

• סדין = masculine singular
• נקי = masculine singular form of clean

Compare:

• סדין נקי = a clean sheet
• שמיכה נקייה = a clean blanket

The adjective changes depending on the noun it describes.

Because שמיכה is a feminine singular noun, so the adjective must also be feminine singular.

So:

• שמיכה = feminine singular
• כחולה = feminine singular form of blue

Compare:

• סדין כחול = a blue sheet (masculine)
• שמיכה כחולה = a blue blanket (feminine)

Again, Hebrew adjectives must agree with the noun.

אבל means but.

It connects the two parts of the sentence:

• הסדין הלבן נקי = the white sheet is clean
• אבל = but
• השמיכה הכחולה עדיין בסל הכביסה = the blue blanket is still in the laundry basket

Its position is very similar to English but.

עדיין means still.

In this sentence, it shows that the situation has not changed yet:

• השמיכה הכחולה עדיין בסל הכביסה
  = the blue blanket is still in the laundry basket

It often appears before the main description or location:

• הוא עדיין בבית = he is still at home
• האוכל עדיין חם = the food is still hot

The preposition ב־ means in / at / inside, and in Hebrew it is usually attached directly to the following word.

So:

• ב + סל = בסל
• meaning: in a basket or in the basket, depending on context

This attachment is very common in Hebrew:

• בבית = in a house / in the house
• בשולחן = on the table or in the table depending on context, though usually context clarifies

In your sentence, בסל הכביסה means in the laundry basket.

This is a construct phrase in Hebrew, called סמיכות.

Structure:

• סל = basket
• הכביסה = the laundry

Together:

• סל הכביסה = literally basket of the laundry
• natural English: the laundry basket

Hebrew often uses this structure where English uses of or a compound noun.

Examples:

• בית ספר = school (literally house of book in older structure)
• כוס מים = a glass of water
• חדר שינה = bedroom (literally room of sleeping)

In a construct phrase, definiteness is often shown on the second word, but it makes the whole phrase definite.

So:

• סל כביסה = a laundry basket
• סל הכביסה = the laundry basket

Even though סל itself does not have ה־, the whole phrase becomes definite because the second word is definite.

This is a very common Hebrew pattern.

It can mean laundry in a broad sense, and the exact meaning depends on context.

It may refer to:

• washed or dirty clothes as laundry
• the general concept of laundry

In סל הכביסה, it means laundry in the sense of clothes that go in that basket, so the whole phrase means laundry basket.

Yes, very much so.

It uses several very common Hebrew features:

• noun + adjective order: השמיכה הכחולה
• no present-tense is: הסדין הלבן נקי
• adjective agreement: כחולה, נקי
• attached prepositions: בסל
• construct phrase: סל הכביסה

So this is a very natural, useful sentence for everyday Hebrew.

The adjectives would change to match each noun.

In your sentence:

• סדין is masculine, so: לבן, נקי
• שמיכה is feminine, so: כחולה

For example:

• המגבת הלבנה נקייה = the white towel is clean
  both adjective forms are feminine singular
• הכיסא הכחול נקי = the blue chair is clean
  adjective forms are masculine singular

So whenever you learn a noun in Hebrew, it is very helpful to learn its gender too.