How to define lstm, units, lags and batch size in keras package

I have data of almost 4700 entries. I have to predict power output. I am unable to understand the algorithm of the LSTM like what is units? how to select units for my data and what are data lags? The code I am using for this work is available here https://www.r-bloggers.com/2018/11/lstm-with-keras-tensorflow/ as I have interest in lstm so I am only using that part of this code.

library(keras)
model <- keras_model_sequential()


model %>%
  layer_lstm(units = 100,
             input_shape = c(datalags, 2),
             batch_size = batch.size,
             return_sequences = TRUE,
             stateful = TRUE) %>%
  layer_dropout(rate = 0.5) %>%
  layer_lstm(units = 50,
             return_sequences = FALSE,
             stateful = TRUE) %>%
  layer_dropout(rate = 0.5) %>%
  layer_dense(units = 1)

model %>%
  compile(loss = 'mae', optimizer = 'adam')

So in this code I am unable to understand

• what is meant by units here?
• What are datalags,

The code uses datalags value as 10, how do I define it for my data? and how to manually select them for my data?