Inflation is an attempt to measure how much less money is worth.
It is a weighted average of some bundle of goods and services price's increase. Money's value is in what you can exchange it for, so higher prices means money is worth less.
Monthly inflation is quoted either as "a year, ending on that month" or "since the previous month". As the values differ by more than a factor of 10, you can usually tell which one is being referred to when they say "inflation in August was 0.4%, a record high" or "inflation in August was 3.6%". You do need some context of the state of the economy, and how surprised the people talking about the numbers are. Sometimes they refer to inflation since the last month, and then annualize it, which adds to the confusion.
"Consumer Inflation"'s value depends on what the basket of goods is, and what you define as the same "good". Is a computer this year the same as the last? If the computer is 10x faster, do you ignore that, or factor it in?
What basket do you use? The typical monthly consumables purchased by a middle class citizen? By a poor citizen? By a rich citizen? A mixture, and if so which mixture?
More detailed inflation figures can focus on inflation facing each quntile of the population by household income, split durable goods from non-durable goods from services, split wage from non-wage inflation, ignore volatile things like food and energy, etc.
Inflation doesn't directly cause prices to raise; instead it is a measure of how much raise in prices happened. It can easily be a self-fullfilling prophesy, as inflation expectations can lead to everyone automatically increasing the price they charge for everything (wages, goods, etc).
Inflation can be viewed as a measurement of the "cost of holding cash". At 10% inflation per year, holding a million dollars in cash for a year costs you 100,000$ in buying power. At 1% inflation it costs 10,000$. At 0.1% inflation, 1000$.
Inflation of 10% in one year, followed by 10% the next, adds up to 1.1*1.1-1 = 21% inflation over the two years. For low inflation numbers this acts a lot like adding; the further from 0% you get the more the lower-order terms make the result larger. 1% inflation for two years adds up to 2.01%, 10% over two years 21%, 100% over two years 300%, 1000% over two years 12000%, etc. (and yes, some places suffer 1000% inflation)