If I want to restore the forum using a backup, do I only need to replace the current database with the backup?

After that the forum will worj as normal?

Should I make the forum inaccessible somehow while doing the backup?

The only program I recommend for restoring mySQL backups, is Bigdump.

Restoring happens very quickly, so most likely you won't need to take additional actions; anyway stopping forums temporary would be a good idea.

So you don't think using cpanel/phpmyadmin is a good idea?

I'll take a look at Bigdump..

phpMyAdmin is not really suitable tool for restoring big-size backups (truly, for making big-size dumps, too). And it works only via web-form, with Bigdump you can upload your dump first somewhere using FTP, then setting options phpMyAdmin doesn't ever have, to restore the back-up smoothly in couple of seconds. It's more "manual and precise" tool IMO.

I'm using this tool in my practice very often and so far I could say the programmer did a great job (it's not an affiliate advertisement ;)

I lost very important topic.. so I have backup from yesterday.. but I don't want lose today's topic and posts.. so how can I restore just that topic ?

Danny2000
It may be difficult for a newbie. You will need to build SQL commands list manually.

Follow backup file (I suppose it is standard plain text backup) and locate this topic's ID in `topics` table backup. SQL string would look like

where TOPIC_ID stands for the numerical ID. Copy the entire INSERT statement into some new plain text file.

Then follow `posts` table backup. Where it says

follow all strings which contain TOPIC_ID as the third value after comma in INSERT statements. Then copy these strings to the new plain text file where you've had topic's statement already.

Then you have to remove TOPIC_ID value from `topics` statement and apply it on your current live forums table. It should insert new topic with its new ID. You have to know this ID and change it in `posts` statements. Then apply all `posts` statements over your live table.