The Dutch r (de r) is not standardised — multiple realisations are used across regions and are all accepted. The three main variants: the alveolar tap or trill (like Spanish r or Italian r — the tongue tip touches the alveolar ridge quickly), common in the south and Belgium; the uvular fricative or trill (like French r or German r — produced at the back of the throat), common in the Randstad and standard Dutch broadcasting; and the approximant (more like American English r — the tongue arches without touching), used in some speakers and in final position.
Which r should you learn? The uvular r (back-of-throat) is the prestige variant in Netherlands Dutch and what you will hear on NOS news, in education, and in Amsterdam. It is produced similarly to the Dutch g but with voicing — the back of the tongue approaches the uvula while the voice is active. If you already produce a uvular r for French or German, transfer that directly to Dutch. If not, the tap/trill is perfectly acceptable and easier for most learners.
R in different positions: initial r (rood — red, rijden — to ride) is typically more strongly realised. Final r after a vowel is often weakened to a schwa or disappears: door (through) sounds like doo-uh, voor (for) like voo-uh, in casual Randstad speech. This vocalisation of final r makes Dutch sound somewhat like non-rhotic British English in these positions. Do not worry about the regional variation early on — choose one r variant, learn it well, and be consistent.