Au supermarché, je prends un sachet de riz et un bocal de sauce tomate.

Au supermarché means at the supermarket or in the supermarket.

French often puts a place expression at the beginning of a sentence to set the scene. So:

• Au supermarché, je prends... = At the supermarket, I take/am taking...

The comma shows that Au supermarché is extra context before the main clause.

Because à + le contracts to au in French.

So:

• à le supermarché → au supermarché

This is a standard contraction:

• à + le = au
• à + les = aux
• de + le = du
• de + les = des

Je prends is the 1st person singular present tense of prendre (to take).

So it means:

• I take
• I am taking
• sometimes, depending on context, I pick up or I get

In this shopping sentence, je prends sounds like I pick up / I take.

Because prendre is an irregular verb, and the je form in the present tense is je prends.

Here are the present tense forms:

• je prends
• tu prends
• il/elle/on prend
• nous prenons
• vous prenez
• ils/elles prennent

So je prends is just the correct verb form for I take.

They are two different container words:

• un sachet = a packet, a sachet, or sometimes a small bag
• un bocal = a jar

So:

• un sachet de riz = a packet of rice
• un bocal de sauce tomate = a jar of tomato sauce

French often uses specific container nouns like this, just as English does.

Here, de means of.

It links the container to what is inside it:

• un sachet de riz = a packet of rice
• un bocal de sauce tomate = a jar of tomato sauce

This is a very common French pattern:

• une bouteille d’eau = a bottle of water
• un verre de lait = a glass of milk
• un kilo de pommes = a kilo of apples

Sauce tomate is the usual fixed expression for tomato sauce.

In French, two nouns can sometimes go together this way, where the second noun describes the first:

• sauce tomate
• jus d’orange
• soupe maison

You may also see sauce à la tomate or other variations in specific contexts, but sauce tomate is the most natural everyday expression here.

Because each noun needs its own article:

• un sachet de riz
• un bocal de sauce tomate

This shows you are taking one packet and one jar.

French normally repeats the article before each separate singular noun in a list like this.

Yes, but the nuance is a little different.

• Au supermarché usually means at the supermarket in a general sense. It is the most natural choice here.
• Dans le supermarché means more literally inside the supermarket.

So both can work, but Au supermarché, je prends... sounds more natural for a simple everyday statement about shopping.

Yes, it is in the present tense.

French present tense often matches several English possibilities, depending on context:

• I take
• I am taking
• sometimes I’m picking up

So je prends does not always translate with just one English form. French uses the present tense more broadly than English sometimes does.

Riz is pronounced roughly like ree.

A few helpful points:

• the r is the French r
• the i sounds like ee
• the final z is silent

So riz sounds like ree, not like the English word rise.

In both parts, the food noun comes after a container expression with de:

• un sachet de riz
• un bocal de sauce tomate

After this kind of de, French usually does not add an article before the food noun.

So you do not say:

• un sachet du riz
• un bocal de la sauce tomate

That would sound wrong here. The structure is simply:

• container + de + item

Yes. Depending on what you want to say, French speakers might also use:

• j’achète = I buy
• je prends = I take / pick up
• je choisis = I choose

The difference is:

• je prends focuses on physically taking the items
• j’achète focuses on the purchase
• je choisis focuses on selecting them

So in a supermarket scene, je prends is very natural.