Listen, repeat, compare. The sounds that cause the most trouble, a repetition exercise with speech recognition and a quiz to train your ear. All sounds, words and sentences are in French.
TL;DR
Listen to the sentence, then repeat it. The words that were recognized turn green.
Bonjour, je voudrais un café, s'il vous plaît.
Listen to the word and choose the one you heard. Each pair differs by only one sound.
For each sound: how to make it, words to listen to, and a sentence to repeat.
/y/ · /u/
English has no « u » sound. Say « i » (like the "ee" in "see") and, without moving your tongue, round your lips forward as if to whistle. « ou » is easier: it is close to the "oo" in "food", but shorter. Mixing them up changes the word: « vu » (seen) and « vous » (you).
/e/ · /ɛ/
« é » is close to the "ay" in "say", but without the glide at the end: keep your mouth still and your lips spread. « è » is more open, like the "e" in "bed". The difference matters for tenses: « j'ai parlé » (passé composé) and « je parlais » (imparfait).
/ə/
In conversation, many « e » are not pronounced: « samedi » sounds like « sam'di ». It works a bit like the vowels English speakers drop in "chocolate" or "every". Dropping these « e » makes your French sound more natural.
/ɑ̃/ · /ɔ̃/ · /ɛ̃/
The air goes through your nose and you do not pronounce an « n »: your tongue never touches the roof of your mouth, unlike in English "on" or "sing". « an » (mouth open), « on » (lips rounded) and « in » (lips spread) are three different sounds: « blanc », « blond », « brin ».
/ʁ/
The French « r » has nothing to do with the English one: the tip of your tongue stays down behind your lower teeth. The sound is made at the back of the throat, like a light, voiced version of the "ch" in Scottish "loch", almost a gargle. Start with « gr » and « tr », which are easier.
When words are closely linked, the final consonant of a word is pronounced before a vowel, a bit like English "an apple": « les amis » (lé-z-amis), « vous avez » (vou-z-avez). No liaison after « et »: « et / un ».
/s/ · /z/
English speakers hear the two sounds easily; the trap is spelling. Between two vowels, a single « s » sounds like « z »: « poison ». A double « ss » sounds like « s »: « poisson » (fish). The difference changes the meaning.
In spoken French, a question can keep the word order of a statement: only your voice rises at the end, as in English "You're coming?". « Tu viens ? » For a statement, your voice goes down.
To practise in test conditions, try the speaking simulator. To hear a specific word, look it up in the dictionary, or review vocabulary by topic.