Here are a few websites to check the pronunciation of a word (and listen to it), both in American and British English:
Tip: /ˌpɒlɪˈtɪʃən/(= politician)
In phonetics, ' corresponds to the syllable which is stressed. So /ˌpɒlɪˈtɪʃən/(= poliTIcian)
You can also use this website, which gives you the "spelled" pronunciation of a word, which means it is not the phonetic transcription but something a bit easier for you to understand! For example, if you check you will find
[pol-i-tish-uh n]
If you want to hear a few words or a sentence, use Acapella Voice Synthesis and pick the accent you would like to practice on.
Finally, if you want to type a text and hear it read by a native speaker, type it here or here. You will then get a recording. Be careful, it's better to type a SHORT text and create two or three recordings than to type a whole text and get a recording in which the speaker speaks too fast! That would not sound natural!
When you're finished, review what we have already learned about American English here and practice for your speech!
Voici un exemple avec le début du discours de Morgane : soit vous utilisez les vrais signes phonétiques, soit vous en inventez, soit vous mixez les deux ! Le but est que cela vous aide et que ce soit lisible pour votre enregistrement !