It's not logically different when you merge from branch to trunk or vice-verse.
Follow these steps for merging code from branch to trunk (Basic merging)-
Checkout the working copy of the trunk (Destination, where the merge is to be done).
Right Click on the Trunk and select TortoiseSVN > Merge
select the First option "Merge a Range of revisions"
Select the Branch URL to merge from.
For Revision range to merge, click on show log. It will show you the complete change log of the branch. Select all the revision that you want to merge (Ctrl+A) for all of them and select OK.
In the next dialog box, select Test Merge. It will show you the Test merge results, you can check if there are any conflicts or the merge is clean.
Finally, Merge.
This process will merge all the branch changes in your trunk's working copy (Local checkout). You need to commit the code after that.
Also, in case of conflicts, TortoiseSVN will automatically give you option to "Edit Conflicts" to resolve them using SVN Editor or leave them so they you can manually resolve them.
Hope this helps.