求翻译：广告主要有两种形式，商业广告是一种人们为了推销某种产品或服务而花钱做的广告；另一种是公益广告，往往免费投放，其目的是就健康，安全或者其他影响到公共利益的问题对人们进行教育。是什么意思？

There are two main forms of advertising, commercial advertising is a people to spend money in order to market a product or service advertisement; the other is the public service ads, free delivery, with the aim of health, safety or other issues affecting the interests of public education to the people.