【中文版】

证券公司是专门从事证券业务的金融机构，其经营范围包括证券经纪、证券自营、证券承销等。证券公司的主要业务是代理客户买卖证券，从事中介业务，并从中收取佣金。此外，证券公司还可以从事自营买卖、承销发行、代理发行、交易推荐、企业重组、收购兼并等业务。

证券公司的经纪业务是代理客户买卖证券，从事中介业务。证券公司接受客户委托，按照客户要求进行买卖证券，并从中收取佣金。此外，证券公司还提供投资咨询、财务顾问等服务。

自营买卖是证券公司为了自身利益进行的买卖行为。证券公司可以运用自有资金或依法筹集的资金进行证券的自营买卖，以获取投资收益。

承销发行是证券公司的一项重要业务。当一家企业要发行股票或债券时，需要有一个承销商来协助它完成发行。证券公司作为承销商，可以为企业提供发行方案、路演安排、定价、分销等全方位的服务。

总之，证券公司是专门从事证券业务的金融机构，其主要业务包括经纪、自营、承销等。证券公司为企业和投资者提供全方位的服务，并在金融市场上扮演着重要的角色。

【英文版】

Securities companies are financial institutions specializing in securities business, including securities brokerage, securities proprietary trading, securities underwriting, etc. The main business of securities companies is to act as agents for customers to buy and sell securities, engaging in intermediary business and collecting commissions. In addition, securities companies can also engage in proprietary trading, underwriting and recommending securities transactions, corporate重组, mergers and acquisitions, etc.

Brokerage business is the main business of securities companies, acting as agents for customers to buy and sell securities and engaging in intermediary business. Securities companies accept customers' appointments, trade securities according to customers' requirements, and collect commissions. In addition, securities companies also provide investment counseling, financial advice and other services.

Proprietary trading is a trading behavior carried out by securities companies for their own benefit. Securities companies can use their own funds or funds raised in accordance with the law to carry out proprietary trading of securities to obtain investment returns.

Underwriting issuance is an important business of securities companies. When a company wants to issue stocks or bonds, it needs a sponsor to assist it in completing the issuance. As an underwriter, a securities company can provide the company with a full range of services such as issuance plans, roadshow arrangements, pricing, and distribution.

In summary, securities companies are financial institutions specializing in securities business. Their main businesses include brokerage, proprietary trading, underwriting, etc. Securities companies provide full-range services to companies and investors and play an important role in the financial market.