STR 25 Bb-Trumpet : Great Beginners Trumpet

I haven't played trumpet for over 20 years, and felt the urge growing to start again over the past year, finally I bought this one as it is for a great price.

Everything's great, the only downsides I found are;

- The "D"Slider goes quite stiff,

- The valves sometimes come up too "slowly" , but Im'not sure if this is because of the way that I press the valves or because they're a bit wonky.

As for the sound I can definitely not produce the sounds given in the example of the site, but once again that could be because I'm very "rusty" at playing the trumpet, it is my first week of having this trumpet and I haven't played since I was 12 years old. so over 20 years ago.