I used to play it back in the day, and compared to modern 1.6 shooters, it really seems wild now. The physics are completely different, forget about holding down the left mouse button while moving- you'll just end up shooting at the sky. Best is, stop, then shoot. Try to fire in short bursts of two to three bullets. If the enemy is far away, fire one bullet at a time. Where did you download the game, by the way? I recommend checking out
https://csget.me/ . The bots are set up properly there, so you can practice shooting at targets. Plus, there’s a short guide on the site that might help clarify some things for you. As for purchasing, all Old Believers use the numbers on the keyboard. For example, B-4-2 is a AK-47. Experiment with this, and over time, you'll figure out which buttons buy which gear.