Just to prove you don’t need expensive kit to make wildlife images, here’s one I took several years back at Pulborough Brooks RSPB reserve in Sussex using a Canon 350D and a Sigma 170-500mm. I used that lens for quite a while for birds in my back garden and on trips, and while it was a bit noisy for my liking, it certainly got me started. I bought it on ebay for a fraction of the £500 or so cost in those days.
Of course, the important thing is field craft which is necessary even when you have one of the larger telephoto lenses. Robins are a good place to start, they’re quite plucky and if you treat them well and don’t make any loud noises or sharp movements, you should be able to gently crawl or even walk towards them and they’ll stick around.
I’ve lost count of the times that I’ve stood in a location watching a robin and it’s got slowly closer checking me out, until the longer telephotos are out of range anyway because the bird has come so close. If you have a regular visitor to your garden, then you can try and tempt it with mealworms from the pet shop. Hold some in your outstretched palm, and once it’s got used to you and knows that you’re not a threat, it will perch on your hand and feed.
Always one of my favourite encounters.