HOW DO BONDS WORK. I WANT TO KNOW HOW THEY FIGURE OUT HOW MUCH MONEY I WILL GET FROM THEM IN 20 YRS?

I have about $1500 dollars in I bonds. How do I know what the lapse is upon them in about twenty years. What else should I deposit in. I am the singular 42 yr aged RN with my kids upon there own.
I have the 403B thru my employer with about $40,000 dollars in it as well as I have about $60, 000 the year. I minister $300 the month to the credit kinship assets account, as well as I am not certain what the change is upon that, substantially not some-more than $1200. I would similar to to have the little investments somewhere, though not certain where to go from here. My home is paid for. It is the dump, though it is mine.