Example - Column span

from tkinter import *

root = Tk()

root.title("Chatting")
root.geometry('300x500')

label_wel = Label(root, text='Welcome')
label_choice = Label(root, text='What would you like to do?')
label_wel.grid(row=0, column=0, columnspan=2)
label_choice.grid(row=1, column=0, columnspan=2)

label_name = Label(root, text='Username')
label_password = Label(root, text='Password')

button_log =  Button(root, text='Login')
button_reg = Button(root, text='Register')

entry_name = Entry(root)
entry_password = Entry(root)

label_name.grid(column=0, row=2)
label_password.grid(column=0, row=3)

entry_name.grid(column=1, row=2)
entry_password.grid(column=1, row=3)

button_log.grid(column=0, row=4)
button_reg.grid(column=1, row=4)

root.mainloop()