Plotting 3 Variables on One Chart - ggplot

I have some experience with base R but am trying to learn tidyverse and ggplot. I have a dataframe with 4 columns of data. I want a simple x-y plot, where the first column of data is on the x-axis, and the data in the other 3 columns is plotted on the y-axis, resulting in 3 lines on one plot. The first 15 lines of my data look like this (sorry about the image - I don't know how to insert a sample of my data):

screen shot - first 15 rows of data

I tried to plot the second and third columns of data as follows: ,

ggplot(data=SWRC_SL, aes(x=SWRC_SL$pressure_head, y=SWRC_SL$UNSODA_theta)) + 
geom_line(colour="red") + scale_x_log10() +
ggplot(data=SWRC_SL, aes(x=SWRC_SL$pressure_head, y=SWRC_SL$Vrugt_theta)) + 
geom_line(colour="blue") + scale_x_log10()

I get this error:

Error: Don't know how to add ggplot(data = SWRC_SL, aes(x = SWRC_SL$pressure_head, y = SWRC_SL$Vrugt_theta)) to a plot

I believe I should be using something like "group=" to indicate which columns should be plotted, but I haven't been able to find an example that shows how you can use gglot to plot data across multiple columns. What am I missing ?