How we can use @font-face in Less

Have you tried putting the font family name in single quotes? The following works just fine for me.

    @font-face {
        font-family: 'cblockbold';
        src: url('assets/fonts/creabbb_-webfont.eot');
        src: url('assets/fonts/creabbb_-webfont.eot?#iefix') format('embedded-opentype'),
             url('assets/fonts/creabbb_-webfont.woff') format('woff'),
             url('assets/fonts/creabbb_-webfont.ttf') format('truetype'),
             url('assets/fonts/creabbb_-webfont.svg#CreativeBlockBBBold') format('svg');
        font-weight: normal;
        font-style: normal;

    }

To use font as a mixin, try:

.ffbasic() {
    font-family: ff-basic-gothic-web-pro-1,ff-basic-gothic-web-pro-2, AppleGothic, "helvetica neue", Arial, sans-serif;
}

then within a style declaration:

.your-class {
     font-size: 14px;
     .ffbasic();    
}