The recommended way of entering most numbers is by using the basic input. Type
"10 to 30"
In order to submit a lognormal distribution with a 5th percentile at 10 and a 95th percentile at 30.
If the first number of these two is negative, then the distribution will be normal.
If you would like to pick a specific distribution and it's corresponding parameters, you can use the function input. If you are entering a distribution, then you will need to refer to call a specific distribution. Here are a few common ones available. A longer list is here.
Estimations proportions or percentages, where the answer must be between 0 and 1.
Most uncertain things, where the uncertainty is symmetric around the median.
Similar to normal, but with a long tail on the right. Cannot be 0 or less.
A flat distribution, where everything inside is equally likely.
Weighted combination of distributions, giving multiple peaks.