This goes at the end to show that you believe what you say, but are not 100% sure. It is also used to show one's opinion. If there is a desu change it to da which is the more casual form and add to omoimasu
1. The speaker is not totally sure of the accuracy of his info...
熊のプーさん は くま だ と 思います。
kuma no pu-san wa kuma da to omoimasu.
Winnie the Pooh is a bear, I think...
Next is an example of showing one's opinion. It is true for the speaker, but may not be so for the listener.
なっとう は おいしい と 思います。
nattou wa oishii to omoimasu.
I think Natto is delicious.
Basically you can say any sentence and if you want to soften it or show you are not sure, or show your opinion add to omoimasu