how to use join in sql

Dear, 

i am working ona tourism website on which users can ask their questions and the other members and post their replies,

i want to know that how can i capture the last reply by (username) and time of posting (timestamp) and i have to use join condition of three tables, i can use max(timestamp) but i am facing problem in using it in join,

 Here is my query,

"select table1.image, table1.status, table2.subject, table2.username, table2.Question_time, table3.reply_time, table3.username from table1,table2,table3"

please suggest me any subquery or any other ideas to get the required result,

Thanks