As far as existing functions go, summary() is a quick way to get various descriptive statistics such as mean, median and min/max values (which can be used for determining outliers) for variables in your dataset.
Taking the example of iris dataset:
>summary(iris)
Sepal.Length Sepal.Width Petal.Length Petal.Width Species
Min. :4.300 Min. :2.000 Min. :1.000 Min. :0.100 setosa :50
1st Qu.:5.100 1st Qu.:2.800 1st Qu.:1.600 1st Qu.:0.300 versicolor:50
Median :5.800 Median :3.000 Median :4.350 Median :1.300 virginica :50
Mean :5.843 Mean :3.057 Mean :3.758 Mean :1.199
3rd Qu.:6.400 3rd Qu.:3.300 3rd Qu.:5.100 3rd Qu.:1.800
Max. :7.900 Max. :4.400 Max. :6.900 Max. :2.500
As for the mode, you'll have to write your own function - you can find some guidance here at Tutorials Point.
One last point, I'd take Sotos's advice, it's really beneficial for yourself and other Stack users.
Thanks!