Totally new to sales

Hello everybody,

I came across this board and was amazed with all the information and support people share.
To start I would like to introduce myself, it will be a long read so I understand if you don't want to read the story.

I'm 30 years old, have very less work experience, one of the reason I suffered from depressions, illness in the past.
I have had some jobs such as simple administration work etc.
Then luck changed and I came across an vacancy of a company who gives people, with a distance to the labour market, a opportunity for work. They were searching for someone to do sales. I got the job and my boss is giving me a lot of freedom, but i have no pressure of hitting targets. I still have a minimal salary but that's reasonable because I have little experience with work let alone sales. But besides that he's very good to me, arranged a car, and nice clothes. I have to sell plastic closures at the moment.

I did bring in an client and some other clients is almost buying (pretty big one). But the thing is, after I called they asked for samples, and because our caps are of a good quality, they decided to buy, It wasn't really me that made the sale, because our caps were tested on jars, and they were about perfect.
Some time ago I called a company and they said we already have a supplier in our country. My boss told me to send samples anyway, I called back and she said I received them but I already have a supplier. Then the conversation ends quickly. How would you guys do the call?

When there is no pressure, I know people like to talk to me. I'm very open, sharp, good sense of humour. Absolutely not to brag at all, but that's the things people say to me. When there is pressure, I'm sounding uncertain, not sharp etc.

I have been watching Jordan Belfort and what he says make sense and I want to take it into practice, but I wonder if for example I could have sold our caps to the company which said they already have a supplier.
I'm so motivated because after years of minimal income, I also would like to earn more. For the moment I don't need tens of thousand, but just double up from what I have in the coming year(s). I realize that's maybe a lousy goal, but when aiming to high I think I end up being disappointing and have less confidence in myself. Yeah self confidence is also an issue.. As long as there is no pressure I look and speak confident.

Would you be so kind to advise me, what books are good, or videos. I know sales is not only theory but it could help.

Thank you so much for reading.