AQA A level chem help - drawing molecules

Hello - Here's a question I was stuck on. the ms link - https://pmt.physicsandmathstutor.com/download/Chemistry/A-level/Topic-Qs/AQA/Organic-II/3.09-Carboxylic-Acids-and-Derivatives/Set-F/Carboxylic%20Acids%20&%20Esters%201%20MS.pdf
(it's question 2c)
(c) Draw the structure of each of the following isomers of C5H8O2
Label each structure you draw with the correct letter L, M, N, P or Q.
L is methyl 2-methylpropenoate.
M is an ester that shows E-Z stereoisomerism.
N is a carboxylic acid with a branched carbon chain and does not show
stereoisomerism.
P is an optically active carboxylic acid.
Q is a cyclic compound that contains a ketone group and has only two peaks in its
1H n.m.r. spectrum. .
The bit where I get stuck is attributing the molecular formula to actual groups. For example, I knew I had a carboxylic group at the end for N - but I wouldn't have figured out that there was also a c=c bond. How would you figure these out? Another difficulty is with L - I seriously struggle to draw out esters purely by names - any tips?

when deducing structures, the first thing to know is the 'back bone' of the compound, e.g the grps present in the compound. then, it is finding the deg of unsaturation of the carbon bonds. for C5H8O2, the 'alkane form' would be C5H12, so the maximum number of bonds formed is 12. with 8H and 2O, the number of bonds left is 2. 2/2 = 1. this means there is 1 deg unsaturation, hence 1 C=C bond in the structure.
otherwise, u can alw draw the aprox structure and then count the number of atoms to ensure that the molecular formula is the same as the one given. (id usually js draw out the structure and count if there are extra hydrogens, esp for compounds with shorter chains)
for esters, the naming is by alcohol carboxylic acid. meaning if it is methyl ethanoate, it is formed by methanol and ethanoic acid. then it wld be drawing the O and double bonds to the correct compounds. the O double bond comes from the acid and O single bond comes from the alcohol. with esters being O-C=O, draw the alcohol/acid grps to whereever they shld belong. it might help to draw the alcohol first, then connect the C=O bond bfr drawing the acid in. with the methyl as a substituent, thatll be the last step - to draw the methyl on the 2nd C for propenoate. also because it is propenoate, it is a propenoic acid, hence a C=C has to be drawn as well
more imptly is to alw check back with the molecular formula given to see if the structure is even correct. if there are extra H, it is likely that there are missing double bond(s)