Learn Finnish: Haluan keskittyä. Älä kuiskaa nyt. - I want to concentrate. Do not whisper now.

To tell someone not to do something, use älä followed by the verb's connegative stem. You can find this stem by taking the 'I' form of the present tense and dropping the -n. For the type 4 verb kuiskata, the 'I' form is kuiskaan. Drop the -n to get kuiskaa, making the command älä kuiskaa.

Does the word älä change if I am speaking to more than one person?

Yes, it does! Älä is the negative imperative for speaking to just one person (singular). If you were telling a group of people not to whisper, you would use the plural form älkää, and the main verb would also change to match (älkää kuiskatko).

Why is keskittyä left in its basic dictionary form?

When you use two verbs together, like 'I want to concentrate', the first verb (haluan) is conjugated to match the subject, while the second verb (keskittyä) stays in its basic dictionary form (the infinitive). This works very similarly to English verb chains.

Why does keskittyä have two 't's here, when the 'I' form is keskityn with only one 't'?