a) First of all, when you suggest me to backup the database does it mean backup both database and transaction log ?
Each backup of the log effectively deletes its contents from the database. However, the ldf file is not shrinked because SQL reuses its space.
You can back it up daily, or even multiple times a day. You can delete the backup files of course (they're in <adnm>\data\backup by default). BTW this folder will be real big now if you haven't deleted its contents yet.
b) What does exactly contain the transaction log files. How often does it need to be backed up ?
It's a standard SQL thing. For a detailed explanation, see e.g.
http://www.winnetmag.com/SQLServer/Article/ArticleID/9792/9792.htmlThe ADNM database was set to recovery mode full which makes the log really large. We'll change this to recovery mode simple in the next update to reduce the size of the log (the trade-off is that the recovery possibilities in case of failure will be somewhat limited).
c) Is it possible to put the ldf files in another path instead of C:\Program Files\Microsoft SQL Server\MSSQL$AVAST\Data i.e. another disk
Sorry, this is not possible without the Enterprise manager (or some programming)
d) What happen if a ldf file is deleted ?
If the database is running, the file will be locked so you won't be able to delete it.