Yes, “犬” and "狗" both mean "dog". However, "犬" is only used in those very formal situation such as scientific passages or some technical terms and it appears only in writing but not in oral Chinese -- we don't say "I have a 犬" or "I will take a 犬 for walk"; instead, we say that "I have a 狗" or "I will take a 狗 for walk" （“我有一条狗”；“我要去遛狗”）

Hi there! You are 50% right! 犬 and 狗 really have the same meaning which is dog. But the difference is that 犬 is the sicentific name of dog while 狗 is the common name. For example, you can see 犬 is written on the signage in the zoo, but we call the animal in the case 狗. By the way, if the dog is very lovely and smart, girls like to call them 狗狗(gou3gou) which means like doggie :)

Yes, they both mean "dog". Technically 犬 are bigger than 狗. But nowadays people simply use 狗 to mean all kinds and sizes of dogs. Only occasionally in some specific writings is 犬 employed.

古代 犬 狗 大有分別 不可混用 http://www.bestory.com/novel/10/104843/39896.html

nowadays 犬 is only used as a part of other words, such as 认狼为犬 or 鸡犬相闻