Can I make something realistic with dynamic shadows.I can’t decide what to use dynamic or lightmass.
It is possible to shadow something realistically with either. There are limitations on both ends and things that will probably cause frustrations when you are not sure what’s going on. We have our Wiki Lighting Troubleshooting guide to help there (linked in my signature below).
Dynamic lighting has the option of using Cascaded Shadow Maps and Distance Field Soft Shadows. At the moment there is no Dynamic Global Illumination, but that is being developed with Distance Field GI. There is LPV for Dynamic GI but it’s not production ready.
Lightmass on the other hand can get good results, but requires a good lightmap UV, understanding of lightmass settings and how to get the best results. It will take some tweaking to get just right, but is great for keeping performance higher by having no overhead for dynamically shadowing your scene. Keep in mind, using static lighting for a very large world is unreasonable. Most machines will run out of memory and cause lightmass to crash or it will take ages because of all the calculations that need to be made for each mesh. If you’ve got a decent sized world you’re building just use Dynamic. 
I hope this helps.
Thank you soo much.It helps a lot. 
no problem. feel free to ask questions anytime. There is a strong and dedicated community here to help out!