For your problem you need to do two things; 1) Find what the nameservers are for ohost.de 2) Set the namservers for your domain at DynaDot.
I have taken a look at ohost.de to try to locate the namservers but I could not locate them. Check your welcome emails from ohost.de to look for the nameservers. They will look something like ns1.ohost.de and ns2.ohost.de. If you cannot find the nameservers in your emails, try ns1.ohost.de and ns2.ohost.de or ask for help in their forums.
Once you have done that you need to get the namservers and 1. Log into your Dynadot account. 2. Click on the "Domains" tab in the main menu. This takes you to the Manage Domain Names page. 3. Click on the link listed in the "Name Server" column. After the page loads, you should see your current name server choice close to the top of the page. 4. Click on the "Name Servers" tab. 5. There are two ways to set your name servers:
To add new name servers, look at Option 1. Enter your two name servers in the provided text boxes, and then click the "Enter Name Servers" button to save your changes.
If you have already entered the name servers for another domain and would like to re-use them, look at Option 2. Choose the name servers from the drop down menus (you can choose up to 10 different name servers), and then click the "Select Name Servers" button to save your changes.