Escriu la contrasenya amb el teclat i no amb el ratolí.

Because escriu is a command form: the tu imperative of escriure (to write).

So Escriu la contrasenya... means Write the password...

A useful thing to know is that in Catalan, the affirmative tu imperative often looks like the ell/ella present form:

• escriu = (he/she) writes / write!

Catalan often leaves out subject pronouns when they are understood from the verb form.

So:

• Escriu la contrasenya = Write the password
• Tu escriu la contrasenya would add emphasis, but it is not normally necessary

This is very common in Catalan, just like in Spanish and Italian.

Because Catalan uses definite articles very naturally before nouns, even in places where English might omit them.

Here:

• la contrasenya = the password

Also, contrasenya is a feminine noun, so it takes la.

Here amb means with, in the sense of using something as a tool.

So:

• amb el teclat = with the keyboard
• amb el ratolí = with the mouse

In English, we might sometimes say using the keyboard. Catalan commonly uses amb for that idea.

Because Catalan normally repeats the preposition when contrasting two things.

So:

• amb el teclat i no amb el ratolí = with the keyboard and not with the mouse

Repeating amb makes the contrast clear and sounds natural. English can sometimes omit the second with, but Catalan usually keeps it here.

Catalan generally prefers the article with concrete countable nouns in this kind of sentence.

So the natural Catalan is:

• amb el teclat
• amb el ratolí

Leaving out the articles would usually sound unnatural here.

Because the second part is an ellipsis: the verb is understood and does not need to be repeated.

The full idea is something like:

• Escriu la contrasenya amb el teclat i no l’escriguis amb el ratolí.

But that is much heavier. In normal Catalan, it is very natural to shorten it to:

• ...i no amb el ratolí

English does the same kind of thing:

• Use the keyboard, not the mouse.

Teclat means keyboard.

It comes from tecla (key), so it is literally the device made of keys. In computer contexts, teclat is the normal word for keyboard.

Ratolí means mouse.

Originally it also means the animal mouse, just like in English, and it is also used for the computer device.

The accent in ratolí shows that the stress falls on the last syllable:

• ra-to-LÍ

So it is pronounced roughly like rah-toh-LEE.

In contrasenya, the ny is pronounced like the ny in canyon, or like Spanish ñ.

So contrasenya sounds roughly like:

• con-tra-SEN-ya

The most important part for an English speaker is:

• ny = a soft ny sound, not a plain n

For a formal singular command, you would use:

• Escrigui la contrasenya amb el teclat i no amb el ratolí.

For an informal plural command (you all):

• Escriviu la contrasenya amb el teclat i no amb el ratolí.

So the original sentence with escriu is specifically the informal singular command: you (one person, informal) write/type...