fission and fusion?

Fusion releases a lot more energy that fission.

Fusion requires a greater activation energy. (fusion bombs use snergy from fission to overcome this.)

Two atomic nuclei are repelled from each other by a very strong electromagnetic force, but if you can get them close enough to each other, the electrostatic force will be overcome by an even stronger force called nuclear force.

You can achieve this energy through particle acceleration or extremely high temperatures.

There are currently plans to build the first fusion reactor producing commercial power in France. This is a multinational effort, and is expected to be completed in a few deacdes.

does nuclear fusion release more energy than nuclear fission?

Yes

is it true that nuclear fusion requires more initial energy for fusion activation?

No

if yes, how is the energy provided in nuclear fusion reactors (i guess there are some experimental ones).