Answer:
1) accentuation 
2) nouns and gender
Step-by-step explanation:
1) 
The monosyllable words (fui, fue, ti, dio, fe, bien ...) do not carry tilde 
The conjunction or when placed between figures is written without tilde: Lo acabaré dentro de 1 o 2 días. 
The word alone never takes tilde, neither when it is adverb (solo sé que no sé nada) nor when it is adjective (está muy solo) 
2) 
The nouns ending in -o make the feminine in -a: al árbitro, la árbitra, el comisario, la comisaria, el filósofo, la filósofa. 
Nouns ending in -a or -e do not change to indicate the feminine: la agente, el agente, el amante, la amante. 
The nouns internet, network and web are feminine: la internet (or internet) la red, la web. 
 
These are some perceptions. I hope I helped you, good luck!