Tonmoy
For 1, open the actual keyword file that the pre/post processor is generating and check every line if there is any keyword that was used especially to solve the system you've modeled.
For 2, if you're using the terminal then you've to install the double precision version from here: https://ftp.lstc.com/user/download_page.html, otherwise if you're on a windows machine then use the LS-run for selecting the version inside it. I don't know about ANSYS though.
For 3, follow the same thing as mentioned here for 2. Otherwise go to youtube and search for some tutorials about LS-Dyna installations. They are extensively mentioned in this page: https://lsdyna.ansys.com/download-install-overview/.
As a new ls-dyna user, I think first you should do some simple analysis which follow closely the problem you have. There are a lot of examples in the dynaexamples.com, which were developed for people like us in mind. Start with something simple and I'd say within a week you'd understand everything that was suggested here.
If you're a visual learner, then you can search problems like yours in youtube. Search with "lsdyna for begineers" there and start from there.
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