I don't believe that fiat cash will disappear in a near future. Always have in mind that you need an internet connection to process digital payments and in many places in the world, the internet infrastructure is not soo good to handle those types of payments.

I think btc as well as other cryptos will jump by the end of this year coz slowly but surely many countries begin to legalize it. And as mentioned before - nothing better isnt invented yet

Hello, I'm not an expert but hope this would help you
1. Find a known and good reputation exchange. Example: Poloniex at Bittrex. Why?
       A.  There are many exchange sites that has many pump & dump coins 
       B.  These kind of exchange have a high standard of accepting coins
       C.  They have huge volume so trades are moving constantly 
2. Find and search about the coin you want to buy. Example: bitcoin, ltc, eth, etc. 
       A.  Pick old coins that still exists and active to date 
       B.  High Market Capitalization
       C.  High Volume in exchange
       D.  Original concepts and active developers
3. Do not buy at the peak price
       A.  Check the daily or weekly details of its high and low trades
       B.  Now the saying "Buy low and Sell High" will took place
       C.  If possible, buy while it still have negative change status if you know the trending will go up
4. Try not to invest in one coin
       A.  You need to have alternative coin in trading so that your investment will not be stucked while waiting for uptrend
5. Do not be swayed easily by trolls 
       A. Do Your Own Research (DYOR)
       
Happy Trading