how to get a nice lawn
 

hi, i am re doing our garden, it was left to over grow,the grass was quite long, we have a lawn mower but it got wet when shed leaked, so now just have a strimer,when i strimmed it it looked all yellow and patchy. should i throw over some grass seeds or re strimmer it, can i just strimmer now on or should i invest in a mower.any advice be well welcome