Recently, when I tried to sing, all my friends said that they could not hear me. But when I talk they can hear me well. I want to know how to resolve this.
If I were in your situation, I'd record myself so I can listen what others hear when I sing. Pretty horrible at first, but very useful. You'd be surprised how much it's actually there that you totally miss by listening only as you perform rather than after you've done it and you're able to focus solely on listening. I used to do it all the time (playing, not singing) and it really worked for me.
I’m not much of a singer, and I can relate to your issue. One thing that's made a huge difference for me is diaphragmatic support. Essentially breathing into your lower abdomen - sticking your gut out instead of puffing out your chest - to support your volume. There are lots of Youtube videos demonstrating and describing this much better than I can.
When I feel like I’m not projecting and/or I’m straining, I stick out my belly and try to relax my chest and throat. Not only does this help me project better, but I can hold notes longer, too.
First of all do you really know how to sing? Have you had voice lessons?
Singing correctly is NOT easy. There is no way that a properly trained voice is quieter than speaking, unless the singer is really singing pianissimo.
Also, your description is so sparse it may not be possible to help you.
One thing I'd mention is that what you describe sounds like an example of your voice not having "support" from your diaphragm. It takes practice to learn how to use your diaphragm correctly, to control your breathing while singing. Untrained people who try to sing sometime hold their breath while singing. I did this too before having lessons with a real vocal coach. You take deep breath and think you have enough to sing but fail to push it out steadily.
The other thing is not having the correct resonance in your head. The sound should really resonate up in the sinus cavity. If it doesn't it will sound very muffled and hitting notes on the high end of your register will be painful, throaty.
Recording yourself or trying to emulate others will not fix these two issues. It takes coaching and practice to get these right but when you get it you should be able to sing at any volume you want with a full rich tone.
Lastly, it is possible that if you know what you are doing you are just nervous. What situation are you singing in where your friends say that they cannot hear you? A chorus, karaoke, band practice? Help us help you with more info.